Auto merge of #46882 - oli-obk:miri3, r=eddyb

Replace all const evaluation with miri

* error reporting in constants prints a stacktrace through all called const fns
* Trivial constant propagation and folding in MIR (always active, irrelevant of the optimization level)
* can now use floating constants in patterns (previously only floating point literals were allowed)
    * the future compat lint is still produced for both cases
* can index into constant arrays during const eval (previously feature gated)
* can create a constant union value with field `a` and read from field `b`
* can dereference references into constants
* can create references inside constants (`const X: &u32 = &22`)
* Tuple struct constructors can be used in constants
* regression in const eval errors spans (some of these need improvements in mir debug info)
* can cast floats to ints and vice versa (in constants, and even nan/inf constants)
* Mir dump prints false/true instead of 0u8/1u8
* `1i8 >> [8][0]` does not lint about exceeding bitshifts anymore.
    * Needs const propagation across projections
* `foo[I]` produces a const eval lint if `foo: [T; N]` and `N < I`
    * Essentially all builtin panics produce lints if they can be statically proven to trigger at runtime. This is on a best effort basis, so there might be some complex cases that don't trigger. (The runtime panic stays there, irrelevant of whether the lint is produced or not)
* can use `union`s to implement `transmute` for `Copy` types in constants without a feature gate. With all the greatness and nasal demons that come with this.
* can convert integers to `&'static T` in constants (useful for embedded)

fixes #34997 (stack overflow with many constants)
fixes #25574 (deref byte strings in patterns)
fixes #27918 (broken mir ICE)
fixes #46114 (ICE on struct constructors in patterns)
fixes #37448 (`SomeStruct { foo } as SomeStruct`)
fixes #43754 (`return` in const fn)
fixes #41898 (tuple struct constructors)
fixes #31364 (infinite recursion with const fn, fixed by miri's recursion limit)
closes #29947 (const indexing stabilization)
fixes #45044 (pattern matching repeat expressions)
fixes #47971 (ICE on const fn + references)
fixes #48081 (ICE on cyclic assoc const error)
fixes #48746 (nonhelpful error message with unions)

r? @eddyb

even though 1k loc are added in tests, this PR reduces the loc in this repository by 700

3 files changed, 7 insertions, 7 deletions

diff --git a/src/test/codegen/consts.rs b/src/test/codegen/consts.rs
index a75b8f3992d..007fb7f4596 100644
--- a/src/test/codegen/consts.rs
+++ b/src/test/codegen/consts.rs
@@ -9,6 +9,7 @@
 // except according to those terms.
 
 // compile-flags: -C no-prepopulate-passes
+// ignore-tidy-linelength
 
 #![crate_type = "lib"]
 
@@ -19,12 +20,11 @@
 // CHECK: @STATIC = {{.*}}, align 4
 
 // This checks the constants from inline_enum_const
-// CHECK: @ref.{{[0-9]+}} = {{.*}}, align 2
+// CHECK: @byte_str.{{[0-9]+}} = {{.*}}, align 2
 
 // This checks the constants from {low,high}_align_const, they share the same
 // constant, but the alignment differs, so the higher one should be used
-// CHECK: [[LOW_HIGH:@ref.[0-9]+]] = {{.*}}, align 4
-// CHECK: [[LOW_HIGH_REF:@const.[0-9]+]] = {{.*}} [[LOW_HIGH]]
+// CHECK: [[LOW_HIGH:@byte_str.[0-9]+]] = {{.*}}, align 4
 
 #[derive(Copy, Clone)]
 
@@ -54,7 +54,7 @@ pub fn inline_enum_const() -> E<i8, i16> {
 #[no_mangle]
 pub fn low_align_const() -> E<i16, [i16; 3]> {
 // Check that low_align_const and high_align_const use the same constant
-// CHECK: load {{.*}} bitcast ({ i16, [0 x i8], i16, [4 x i8] }** [[LOW_HIGH_REF]]
+// CHECK: i8* getelementptr inbounds (<{ [8 x i8] }>, <{ [8 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0),
     *&E::A(0)
 }
 
@@ -62,6 +62,6 @@ pub fn low_align_const() -> E<i16, [i16; 3]> {
 #[no_mangle]
 pub fn high_align_const() -> E<i16, i32> {
 // Check that low_align_const and high_align_const use the same constant
-// CHECK: load {{.*}} bitcast ({ i16, [0 x i8], i16, [4 x i8] }** [[LOW_HIGH_REF]]
+// CHECK: i8* getelementptr inbounds (<{ [8 x i8] }>, <{ [8 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0),
     *&E::A(0)
 }
diff --git a/src/test/codegen/link_section.rs b/src/test/codegen/link_section.rs
index 1879002e7f3..9c56a316b34 100644
--- a/src/test/codegen/link_section.rs
+++ b/src/test/codegen/link_section.rs
@@ -12,7 +12,7 @@
 
 #![crate_type = "lib"]
 
-// CHECK: @VAR1 = constant i32 1, section ".test_one"
+// CHECK: @VAR1 = constant <{ [4 x i8] }> <{ [4 x i8] c"\01\00\00\00" }>, section ".test_one"
 #[no_mangle]
 #[link_section = ".test_one"]
 pub static VAR1: u32 = 1;
diff --git a/src/test/codegen/remap_path_prefix/main.rs b/src/test/codegen/remap_path_prefix/main.rs
index 2f46b6c5d48..4fb8c37558d 100644
--- a/src/test/codegen/remap_path_prefix/main.rs
+++ b/src/test/codegen/remap_path_prefix/main.rs
@@ -22,7 +22,7 @@ mod aux_mod;
 include!("aux_mod.rs");
 
 // Here we check that the expansion of the file!() macro is mapped.
-// CHECK: internal constant [34 x i8] c"/the/src/remap_path_prefix/main.rs"
+// CHECK: @byte_str.1 = private unnamed_addr constant <{ [34 x i8] }> <{ [34 x i8] c"/the/src/remap_path_prefix/main.rs" }>, align 1
 pub static FILE_PATH: &'static str = file!();
 
 fn main() {