Rollup merge of #50819 - cjkenn:cjkenn/div-by-zero, r=kennytm

Fix potential divide by zero

This should fix #50761

I had trouble reproducing with the provided code, but looking at the stack trace would indicate that this code is the likely cause. I made a number of assumptions here, because I don't have enough context on how the register size is set:

1. I assumed `rest.unit.size.bytes()` can be 0, and it's ok if it's set to 0 before this function is called
2. I assumed that if `rest.unit.size.bytes()` is 0, that we want `rest_count` to also be 0.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/librustc_codegen_llvm/abi.rs b/src/librustc_codegen_llvm/abi.rs
index 25c598c532c..221012903d9 100644
--- a/src/librustc_codegen_llvm/abi.rs
+++ b/src/librustc_codegen_llvm/abi.rs
@@ -127,8 +127,12 @@ impl LlvmType for Reg {
 impl LlvmType for CastTarget {
     fn llvm_type(&self, cx: &CodegenCx) -> Type {
         let rest_ll_unit = self.rest.unit.llvm_type(cx);
-        let rest_count = self.rest.total.bytes() / self.rest.unit.size.bytes();
-        let rem_bytes = self.rest.total.bytes() % self.rest.unit.size.bytes();
+        let (rest_count, rem_bytes) = if self.rest.unit.size.bytes() == 0 {
+            (0, 0)
+        } else {
+            (self.rest.total.bytes() / self.rest.unit.size.bytes(),
+            self.rest.total.bytes() % self.rest.unit.size.bytes())
+        };
 
         if self.prefix.iter().all(|x| x.is_none()) {
             // Simplify to a single unit when there is no prefix and size <= unit size