Auto merge of #75370 - simonvandel:optimize-if-condition-on-int-to-switch, r=oli-obk

New pass to optimize `if`conditions on integrals to switches on the integer

Fixes #75144

 Pass to convert `if` conditions on integrals into switches on the integral.
 For an example, it turns something like

 ```
 _3 = Eq(move _4, const 43i32);
 StorageDead(_4);
 switchInt(_3) -> [false: bb2, otherwise: bb3];
 ```

 into:

 ```
 switchInt(_4) -> [43i32: bb3, otherwise: bb2];
 ```

9 files changed, 411 insertions, 0 deletions

diff --git a/src/test/mir-opt/if-condition-int.rs b/src/test/mir-opt/if-condition-int.rs
new file mode 100644
index 00000000000..b34389a0ab5
--- /dev/null
+++ b/src/test/mir-opt/if-condition-int.rs
@@ -0,0 +1,65 @@
+// compile-flags: -O
+// EMIT_MIR if_condition_int.opt_u32.SimplifyComparisonIntegral.diff
+// EMIT_MIR if_condition_int.opt_negative.SimplifyComparisonIntegral.diff
+// EMIT_MIR if_condition_int.opt_char.SimplifyComparisonIntegral.diff
+// EMIT_MIR if_condition_int.opt_i8.SimplifyComparisonIntegral.diff
+// EMIT_MIR if_condition_int.dont_opt_bool.SimplifyComparisonIntegral.diff
+// EMIT_MIR if_condition_int.opt_multiple_ifs.SimplifyComparisonIntegral.diff
+// EMIT_MIR if_condition_int.dont_remove_comparison.SimplifyComparisonIntegral.diff
+// EMIT_MIR if_condition_int.dont_opt_floats.SimplifyComparisonIntegral.diff
+
+fn opt_u32(x: u32) -> u32 {
+    if x == 42 { 0 } else { 1 }
+}
+
+// don't opt: it is already optimal to switch on the bool
+fn dont_opt_bool(x: bool) -> u32 {
+    if x { 0 } else { 1 }
+}
+
+fn opt_char(x: char) -> u32 {
+    if x == 'x' { 0 } else { 1 }
+}
+
+fn opt_i8(x: i8) -> u32 {
+    if x == 42 { 0 } else { 1 }
+}
+
+fn opt_negative(x: i32) -> u32 {
+    if x == -42 { 0 } else { 1 }
+}
+
+fn opt_multiple_ifs(x: u32) -> u32 {
+    if x == 42 {
+        0
+    } else if x != 21 {
+        1
+    } else {
+        2
+    }
+}
+
+// test that we optimize, but do not remove the b statement, as that is used later on
+fn dont_remove_comparison(a: i8) -> i32 {
+    let b = a == 17;
+    match b {
+        false => 10 + b as i32,
+        true => 100 + b as i32,
+    }
+}
+
+// test that we do not optimize on floats
+fn dont_opt_floats(a: f32) -> i32 {
+    if a == -42.0 { 0 } else { 1 }
+}
+
+fn main() {
+    opt_u32(0);
+    opt_char('0');
+    opt_i8(22);
+    dont_opt_bool(false);
+    opt_negative(0);
+    opt_multiple_ifs(0);
+    dont_remove_comparison(11);
+    dont_opt_floats(1.0);
+}
diff --git a/src/test/mir-opt/if_condition_int.dont_opt_bool.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.dont_opt_bool.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..993ff660caa
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.dont_opt_bool.SimplifyComparisonIntegral.diff
@@ -0,0 +1,30 @@
+- // MIR for `dont_opt_bool` before SimplifyComparisonIntegral
++ // MIR for `dont_opt_bool` after SimplifyComparisonIntegral
+  
+  fn dont_opt_bool(_1: bool) -> u32 {
+      debug x => _1;                       // in scope 0 at $DIR/if-condition-int.rs:16:18: 16:19
+      let mut _0: u32;                     // return place in scope 0 at $DIR/if-condition-int.rs:16:30: 16:33
+      let mut _2: bool;                    // in scope 0 at $DIR/if-condition-int.rs:17:8: 17:9
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:17:8: 17:9
+          _2 = _1;                         // scope 0 at $DIR/if-condition-int.rs:17:8: 17:9
+          switchInt(_2) -> [false: bb1, otherwise: bb2]; // scope 0 at $DIR/if-condition-int.rs:17:5: 17:26
+      }
+  
+      bb1: {
+          _0 = const 1_u32;                // scope 0 at $DIR/if-condition-int.rs:17:23: 17:24
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:17:5: 17:26
+      }
+  
+      bb2: {
+          _0 = const 0_u32;                // scope 0 at $DIR/if-condition-int.rs:17:12: 17:13
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:17:5: 17:26
+      }
+  
+      bb3: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:18:1: 18:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:18:2: 18:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/if_condition_int.dont_opt_floats.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.dont_opt_floats.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..8ae9168c950
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.dont_opt_floats.SimplifyComparisonIntegral.diff
@@ -0,0 +1,37 @@
+- // MIR for `dont_opt_floats` before SimplifyComparisonIntegral
++ // MIR for `dont_opt_floats` after SimplifyComparisonIntegral
+  
+  fn dont_opt_floats(_1: f32) -> i32 {
+      debug a => _1;                       // in scope 0 at $DIR/if-condition-int.rs:52:20: 52:21
+      let mut _0: i32;                     // return place in scope 0 at $DIR/if-condition-int.rs:52:31: 52:34
+      let mut _2: bool;                    // in scope 0 at $DIR/if-condition-int.rs:53:8: 53:18
+      let mut _3: f32;                     // in scope 0 at $DIR/if-condition-int.rs:53:8: 53:9
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:53:8: 53:18
+          StorageLive(_3);                 // scope 0 at $DIR/if-condition-int.rs:53:8: 53:9
+          _3 = _1;                         // scope 0 at $DIR/if-condition-int.rs:53:8: 53:9
+          _2 = Eq(move _3, const -42f32);  // scope 0 at $DIR/if-condition-int.rs:53:8: 53:18
+                                           // mir::Constant
+                                           // + span: $DIR/if-condition-int.rs:53:13: 53:18
+                                           // + literal: Const { ty: f32, val: Value(Scalar(0xc2280000)) }
+          StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:53:17: 53:18
+          switchInt(_2) -> [false: bb1, otherwise: bb2]; // scope 0 at $DIR/if-condition-int.rs:53:5: 53:35
+      }
+  
+      bb1: {
+          _0 = const 1_i32;                // scope 0 at $DIR/if-condition-int.rs:53:32: 53:33
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:53:5: 53:35
+      }
+  
+      bb2: {
+          _0 = const 0_i32;                // scope 0 at $DIR/if-condition-int.rs:53:21: 53:22
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:53:5: 53:35
+      }
+  
+      bb3: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:54:1: 54:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:54:2: 54:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/if_condition_int.dont_remove_comparison.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.dont_remove_comparison.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..b590be5370f
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.dont_remove_comparison.SimplifyComparisonIntegral.diff
@@ -0,0 +1,58 @@
+- // MIR for `dont_remove_comparison` before SimplifyComparisonIntegral
++ // MIR for `dont_remove_comparison` after SimplifyComparisonIntegral
+  
+  fn dont_remove_comparison(_1: i8) -> i32 {
+      debug a => _1;                       // in scope 0 at $DIR/if-condition-int.rs:43:27: 43:28
+      let mut _0: i32;                     // return place in scope 0 at $DIR/if-condition-int.rs:43:37: 43:40
+      let _2: bool;                        // in scope 0 at $DIR/if-condition-int.rs:44:9: 44:10
+      let mut _3: i8;                      // in scope 0 at $DIR/if-condition-int.rs:44:13: 44:14
+      let mut _4: i32;                     // in scope 0 at $DIR/if-condition-int.rs:46:23: 46:31
+      let mut _5: bool;                    // in scope 0 at $DIR/if-condition-int.rs:46:23: 46:24
+      let mut _6: i32;                     // in scope 0 at $DIR/if-condition-int.rs:47:23: 47:31
+      let mut _7: bool;                    // in scope 0 at $DIR/if-condition-int.rs:47:23: 47:24
+      scope 1 {
+          debug b => _2;                   // in scope 1 at $DIR/if-condition-int.rs:44:9: 44:10
+      }
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:44:9: 44:10
+          StorageLive(_3);                 // scope 0 at $DIR/if-condition-int.rs:44:13: 44:14
+          _3 = _1;                         // scope 0 at $DIR/if-condition-int.rs:44:13: 44:14
+-         _2 = Eq(move _3, const 17_i8);   // scope 0 at $DIR/if-condition-int.rs:44:13: 44:20
+-         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:44:19: 44:20
+-         switchInt(_2) -> [false: bb2, otherwise: bb1]; // scope 1 at $DIR/if-condition-int.rs:46:9: 46:14
++         _2 = Eq(_3, const 17_i8);        // scope 0 at $DIR/if-condition-int.rs:44:13: 44:20
++         nop;                             // scope 0 at $DIR/if-condition-int.rs:44:19: 44:20
++         switchInt(move _3) -> [17_i8: bb1, otherwise: bb2]; // scope 1 at $DIR/if-condition-int.rs:46:9: 46:14
+      }
+  
+      bb1: {
++         StorageDead(_3);                 // scope 1 at $DIR/if-condition-int.rs:46:9: 46:14
+          StorageLive(_6);                 // scope 1 at $DIR/if-condition-int.rs:47:23: 47:31
+          StorageLive(_7);                 // scope 1 at $DIR/if-condition-int.rs:47:23: 47:24
+          _7 = _2;                         // scope 1 at $DIR/if-condition-int.rs:47:23: 47:24
+          _6 = move _7 as i32 (Misc);      // scope 1 at $DIR/if-condition-int.rs:47:23: 47:31
+          StorageDead(_7);                 // scope 1 at $DIR/if-condition-int.rs:47:30: 47:31
+          _0 = Add(const 100_i32, move _6); // scope 1 at $DIR/if-condition-int.rs:47:17: 47:31
+          StorageDead(_6);                 // scope 1 at $DIR/if-condition-int.rs:47:30: 47:31
+          goto -> bb3;                     // scope 1 at $DIR/if-condition-int.rs:45:5: 48:6
+      }
+  
+      bb2: {
++         StorageDead(_3);                 // scope 1 at $DIR/if-condition-int.rs:46:9: 46:14
+          StorageLive(_4);                 // scope 1 at $DIR/if-condition-int.rs:46:23: 46:31
+          StorageLive(_5);                 // scope 1 at $DIR/if-condition-int.rs:46:23: 46:24
+          _5 = _2;                         // scope 1 at $DIR/if-condition-int.rs:46:23: 46:24
+          _4 = move _5 as i32 (Misc);      // scope 1 at $DIR/if-condition-int.rs:46:23: 46:31
+          StorageDead(_5);                 // scope 1 at $DIR/if-condition-int.rs:46:30: 46:31
+          _0 = Add(const 10_i32, move _4); // scope 1 at $DIR/if-condition-int.rs:46:18: 46:31
+          StorageDead(_4);                 // scope 1 at $DIR/if-condition-int.rs:46:30: 46:31
+          goto -> bb3;                     // scope 1 at $DIR/if-condition-int.rs:45:5: 48:6
+      }
+  
+      bb3: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:49:1: 49:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:49:2: 49:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/if_condition_int.opt_char.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.opt_char.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..ae0960028a8
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.opt_char.SimplifyComparisonIntegral.diff
@@ -0,0 +1,39 @@
+- // MIR for `opt_char` before SimplifyComparisonIntegral
++ // MIR for `opt_char` after SimplifyComparisonIntegral
+  
+  fn opt_char(_1: char) -> u32 {
+      debug x => _1;                       // in scope 0 at $DIR/if-condition-int.rs:20:13: 20:14
+      let mut _0: u32;                     // return place in scope 0 at $DIR/if-condition-int.rs:20:25: 20:28
+      let mut _2: bool;                    // in scope 0 at $DIR/if-condition-int.rs:21:8: 21:16
+      let mut _3: char;                    // in scope 0 at $DIR/if-condition-int.rs:21:8: 21:9
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:21:8: 21:16
+          StorageLive(_3);                 // scope 0 at $DIR/if-condition-int.rs:21:8: 21:9
+          _3 = _1;                         // scope 0 at $DIR/if-condition-int.rs:21:8: 21:9
+-         _2 = Eq(move _3, const 'x');     // scope 0 at $DIR/if-condition-int.rs:21:8: 21:16
+-         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:21:15: 21:16
+-         switchInt(_2) -> [false: bb1, otherwise: bb2]; // scope 0 at $DIR/if-condition-int.rs:21:5: 21:33
++         _2 = Eq(_3, const 'x');          // scope 0 at $DIR/if-condition-int.rs:21:8: 21:16
++         nop;                             // scope 0 at $DIR/if-condition-int.rs:21:15: 21:16
++         switchInt(move _3) -> ['x': bb2, otherwise: bb1]; // scope 0 at $DIR/if-condition-int.rs:21:5: 21:33
+      }
+  
+      bb1: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:21:5: 21:33
+          _0 = const 1_u32;                // scope 0 at $DIR/if-condition-int.rs:21:30: 21:31
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:21:5: 21:33
+      }
+  
+      bb2: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:21:5: 21:33
+          _0 = const 0_u32;                // scope 0 at $DIR/if-condition-int.rs:21:19: 21:20
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:21:5: 21:33
+      }
+  
+      bb3: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:22:1: 22:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:22:2: 22:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/if_condition_int.opt_i8.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.opt_i8.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..8d59e51ac2b
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.opt_i8.SimplifyComparisonIntegral.diff
@@ -0,0 +1,39 @@
+- // MIR for `opt_i8` before SimplifyComparisonIntegral
++ // MIR for `opt_i8` after SimplifyComparisonIntegral
+  
+  fn opt_i8(_1: i8) -> u32 {
+      debug x => _1;                       // in scope 0 at $DIR/if-condition-int.rs:24:11: 24:12
+      let mut _0: u32;                     // return place in scope 0 at $DIR/if-condition-int.rs:24:21: 24:24
+      let mut _2: bool;                    // in scope 0 at $DIR/if-condition-int.rs:25:8: 25:15
+      let mut _3: i8;                      // in scope 0 at $DIR/if-condition-int.rs:25:8: 25:9
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:25:8: 25:15
+          StorageLive(_3);                 // scope 0 at $DIR/if-condition-int.rs:25:8: 25:9
+          _3 = _1;                         // scope 0 at $DIR/if-condition-int.rs:25:8: 25:9
+-         _2 = Eq(move _3, const 42_i8);   // scope 0 at $DIR/if-condition-int.rs:25:8: 25:15
+-         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:25:14: 25:15
+-         switchInt(_2) -> [false: bb1, otherwise: bb2]; // scope 0 at $DIR/if-condition-int.rs:25:5: 25:32
++         _2 = Eq(_3, const 42_i8);        // scope 0 at $DIR/if-condition-int.rs:25:8: 25:15
++         nop;                             // scope 0 at $DIR/if-condition-int.rs:25:14: 25:15
++         switchInt(move _3) -> [42_i8: bb2, otherwise: bb1]; // scope 0 at $DIR/if-condition-int.rs:25:5: 25:32
+      }
+  
+      bb1: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:25:5: 25:32
+          _0 = const 1_u32;                // scope 0 at $DIR/if-condition-int.rs:25:29: 25:30
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:25:5: 25:32
+      }
+  
+      bb2: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:25:5: 25:32
+          _0 = const 0_u32;                // scope 0 at $DIR/if-condition-int.rs:25:18: 25:19
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:25:5: 25:32
+      }
+  
+      bb3: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:26:1: 26:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:26:2: 26:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/if_condition_int.opt_multiple_ifs.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.opt_multiple_ifs.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..c4975661efe
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.opt_multiple_ifs.SimplifyComparisonIntegral.diff
@@ -0,0 +1,65 @@
+- // MIR for `opt_multiple_ifs` before SimplifyComparisonIntegral
++ // MIR for `opt_multiple_ifs` after SimplifyComparisonIntegral
+  
+  fn opt_multiple_ifs(_1: u32) -> u32 {
+      debug x => _1;                       // in scope 0 at $DIR/if-condition-int.rs:32:21: 32:22
+      let mut _0: u32;                     // return place in scope 0 at $DIR/if-condition-int.rs:32:32: 32:35
+      let mut _2: bool;                    // in scope 0 at $DIR/if-condition-int.rs:33:8: 33:15
+      let mut _3: u32;                     // in scope 0 at $DIR/if-condition-int.rs:33:8: 33:9
+      let mut _4: bool;                    // in scope 0 at $DIR/if-condition-int.rs:35:15: 35:22
+      let mut _5: u32;                     // in scope 0 at $DIR/if-condition-int.rs:35:15: 35:16
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:33:8: 33:15
+          StorageLive(_3);                 // scope 0 at $DIR/if-condition-int.rs:33:8: 33:9
+          _3 = _1;                         // scope 0 at $DIR/if-condition-int.rs:33:8: 33:9
+-         _2 = Eq(move _3, const 42_u32);  // scope 0 at $DIR/if-condition-int.rs:33:8: 33:15
+-         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:33:14: 33:15
+-         switchInt(_2) -> [false: bb1, otherwise: bb2]; // scope 0 at $DIR/if-condition-int.rs:33:5: 39:6
++         _2 = Eq(_3, const 42_u32);       // scope 0 at $DIR/if-condition-int.rs:33:8: 33:15
++         nop;                             // scope 0 at $DIR/if-condition-int.rs:33:14: 33:15
++         switchInt(move _3) -> [42_u32: bb2, otherwise: bb1]; // scope 0 at $DIR/if-condition-int.rs:33:5: 39:6
+      }
+  
+      bb1: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:33:5: 39:6
+          StorageLive(_4);                 // scope 0 at $DIR/if-condition-int.rs:35:15: 35:22
+          StorageLive(_5);                 // scope 0 at $DIR/if-condition-int.rs:35:15: 35:16
+          _5 = _1;                         // scope 0 at $DIR/if-condition-int.rs:35:15: 35:16
+-         _4 = Ne(move _5, const 21_u32);  // scope 0 at $DIR/if-condition-int.rs:35:15: 35:22
+-         StorageDead(_5);                 // scope 0 at $DIR/if-condition-int.rs:35:21: 35:22
+-         switchInt(_4) -> [false: bb3, otherwise: bb4]; // scope 0 at $DIR/if-condition-int.rs:35:12: 39:6
++         _4 = Ne(_5, const 21_u32);       // scope 0 at $DIR/if-condition-int.rs:35:15: 35:22
++         nop;                             // scope 0 at $DIR/if-condition-int.rs:35:21: 35:22
++         switchInt(move _5) -> [21_u32: bb3, otherwise: bb4]; // scope 0 at $DIR/if-condition-int.rs:35:12: 39:6
+      }
+  
+      bb2: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:33:5: 39:6
+          _0 = const 0_u32;                // scope 0 at $DIR/if-condition-int.rs:34:9: 34:10
+          goto -> bb6;                     // scope 0 at $DIR/if-condition-int.rs:33:5: 39:6
+      }
+  
+      bb3: {
++         StorageDead(_5);                 // scope 0 at $DIR/if-condition-int.rs:35:12: 39:6
+          _0 = const 2_u32;                // scope 0 at $DIR/if-condition-int.rs:38:9: 38:10
+          goto -> bb5;                     // scope 0 at $DIR/if-condition-int.rs:35:12: 39:6
+      }
+  
+      bb4: {
++         StorageDead(_5);                 // scope 0 at $DIR/if-condition-int.rs:35:12: 39:6
+          _0 = const 1_u32;                // scope 0 at $DIR/if-condition-int.rs:36:9: 36:10
+          goto -> bb5;                     // scope 0 at $DIR/if-condition-int.rs:35:12: 39:6
+      }
+  
+      bb5: {
+          StorageDead(_4);                 // scope 0 at $DIR/if-condition-int.rs:39:5: 39:6
+          goto -> bb6;                     // scope 0 at $DIR/if-condition-int.rs:33:5: 39:6
+      }
+  
+      bb6: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:40:1: 40:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:40:2: 40:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/if_condition_int.opt_negative.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.opt_negative.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..d7f544e44c0
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.opt_negative.SimplifyComparisonIntegral.diff
@@ -0,0 +1,39 @@
+- // MIR for `opt_negative` before SimplifyComparisonIntegral
++ // MIR for `opt_negative` after SimplifyComparisonIntegral
+  
+  fn opt_negative(_1: i32) -> u32 {
+      debug x => _1;                       // in scope 0 at $DIR/if-condition-int.rs:28:17: 28:18
+      let mut _0: u32;                     // return place in scope 0 at $DIR/if-condition-int.rs:28:28: 28:31
+      let mut _2: bool;                    // in scope 0 at $DIR/if-condition-int.rs:29:8: 29:16
+      let mut _3: i32;                     // in scope 0 at $DIR/if-condition-int.rs:29:8: 29:9
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:29:8: 29:16
+          StorageLive(_3);                 // scope 0 at $DIR/if-condition-int.rs:29:8: 29:9
+          _3 = _1;                         // scope 0 at $DIR/if-condition-int.rs:29:8: 29:9
+-         _2 = Eq(move _3, const -42_i32); // scope 0 at $DIR/if-condition-int.rs:29:8: 29:16
+-         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:29:15: 29:16
+-         switchInt(_2) -> [false: bb1, otherwise: bb2]; // scope 0 at $DIR/if-condition-int.rs:29:5: 29:33
++         _2 = Eq(_3, const -42_i32);      // scope 0 at $DIR/if-condition-int.rs:29:8: 29:16
++         nop;                             // scope 0 at $DIR/if-condition-int.rs:29:15: 29:16
++         switchInt(move _3) -> [-42_i32: bb2, otherwise: bb1]; // scope 0 at $DIR/if-condition-int.rs:29:5: 29:33
+      }
+  
+      bb1: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:29:5: 29:33
+          _0 = const 1_u32;                // scope 0 at $DIR/if-condition-int.rs:29:30: 29:31
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:29:5: 29:33
+      }
+  
+      bb2: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:29:5: 29:33
+          _0 = const 0_u32;                // scope 0 at $DIR/if-condition-int.rs:29:19: 29:20
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:29:5: 29:33
+      }
+  
+      bb3: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:30:1: 30:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:30:2: 30:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/if_condition_int.opt_u32.SimplifyComparisonIntegral.diff b/src/test/mir-opt/if_condition_int.opt_u32.SimplifyComparisonIntegral.diff
new file mode 100644
index 00000000000..51e00e680c2
--- /dev/null
+++ b/src/test/mir-opt/if_condition_int.opt_u32.SimplifyComparisonIntegral.diff
@@ -0,0 +1,39 @@
+- // MIR for `opt_u32` before SimplifyComparisonIntegral
++ // MIR for `opt_u32` after SimplifyComparisonIntegral
+  
+  fn opt_u32(_1: u32) -> u32 {
+      debug x => _1;                       // in scope 0 at $DIR/if-condition-int.rs:11:12: 11:13
+      let mut _0: u32;                     // return place in scope 0 at $DIR/if-condition-int.rs:11:23: 11:26
+      let mut _2: bool;                    // in scope 0 at $DIR/if-condition-int.rs:12:8: 12:15
+      let mut _3: u32;                     // in scope 0 at $DIR/if-condition-int.rs:12:8: 12:9
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/if-condition-int.rs:12:8: 12:15
+          StorageLive(_3);                 // scope 0 at $DIR/if-condition-int.rs:12:8: 12:9
+          _3 = _1;                         // scope 0 at $DIR/if-condition-int.rs:12:8: 12:9
+-         _2 = Eq(move _3, const 42_u32);  // scope 0 at $DIR/if-condition-int.rs:12:8: 12:15
+-         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:12:14: 12:15
+-         switchInt(_2) -> [false: bb1, otherwise: bb2]; // scope 0 at $DIR/if-condition-int.rs:12:5: 12:32
++         _2 = Eq(_3, const 42_u32);       // scope 0 at $DIR/if-condition-int.rs:12:8: 12:15
++         nop;                             // scope 0 at $DIR/if-condition-int.rs:12:14: 12:15
++         switchInt(move _3) -> [42_u32: bb2, otherwise: bb1]; // scope 0 at $DIR/if-condition-int.rs:12:5: 12:32
+      }
+  
+      bb1: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:12:5: 12:32
+          _0 = const 1_u32;                // scope 0 at $DIR/if-condition-int.rs:12:29: 12:30
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:12:5: 12:32
+      }
+  
+      bb2: {
++         StorageDead(_3);                 // scope 0 at $DIR/if-condition-int.rs:12:5: 12:32
+          _0 = const 0_u32;                // scope 0 at $DIR/if-condition-int.rs:12:18: 12:19
+          goto -> bb3;                     // scope 0 at $DIR/if-condition-int.rs:12:5: 12:32
+      }
+  
+      bb3: {
+          StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:13:1: 13:2
+          return;                          // scope 0 at $DIR/if-condition-int.rs:13:2: 13:2
+      }
+  }
+