[llvm] [InstCombine] Add an option to skip simplification on call instruction where a non-void return value is expected while the callee returns void (PR #98536)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (yozhu)

<details>
<summary>Changes</summary>

Add an option to skip simplification on call instruction where a non-void
return value is expected but the callee returns void, which is undefined
behavior and can lead to non-determinism runtime behaviors or crashes.

---
Full diff: https://github.com/llvm/llvm-project/pull/98536.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+6-1) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 0ca56f08c333d..880932159f570 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -89,6 +89,11 @@ static cl::opt<unsigned> GuardWideningWindow(
     cl::desc("How wide an instruction window to bypass looking for "
              "another guard"));
 
+static cl::opt<bool> SkipRetTypeVoidToNonVoidCallInst(
+    "instcombine-skip-call-ret-type-void-to-nonvoid", cl::init(false),
+    cl::desc("skip simplifying call instruction which expects a non-void "
+             "return value but the callee returns void"));
+
 /// Return the specified type promoted as it would be to pass though a va_arg
 /// area.
 static Type *getPromotedType(Type *Ty) {
@@ -4073,7 +4078,7 @@ bool InstCombinerImpl::transformConstExprCastCall(CallBase &Call) {
 
       if (!Caller->use_empty() &&
           // void -> non-void is handled specially
-          !NewRetTy->isVoidTy())
+          (SkipRetTypeVoidToNonVoidCallInst || !NewRetTy->isVoidTy()))
         return false;   // Cannot transform this return value.
     }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/98536