[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]

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

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.

>From 03bb6f3b5d309c9dd9f0c901ca006783ca98bfca Mon Sep 17 00:00:00 2001
From: YongKang Zhu <yongzhu at fb.com>
Date: Thu, 11 Jul 2024 13:20:54 -0700
Subject: [PATCH] [InstCombine] Add an option to not take advantage of void to
 non-void conversion on return value

---
 llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

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.
     }