[InstCombine] Fix unsafe PHINode cast and simplify logic in PointerReplacer

[milos1397]

Handles issue #171883

Basically, if the operand of the $\phi$ is an Instruction but it's not available, the condition would just break, and when we reach the deferral check, execution would continue even though there is a non-Instruction operand, leading to a crash in the subsequent processing loop.

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[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Miloš Poletanović (milos1397)

Changes

Handles issue #171883

Basically, if the operand of the $\phi$ is an Instruction but it's not available, the condition would just break, and when we reach the deferral check, execution would continue even though there is a non-Instruction operand, leading to a crash in the subsequent processing loop.

---

Full diff: https://github.com/llvm/llvm-project/pull/172332.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp (+6-6)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 9491610190c10..ea5587f4c9412 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -296,12 +296,12 @@ bool PointerReplacer::collectUsers() {
       /// TODO: Handle poison and null pointers for PHI and select.
       // If all incoming values are available, mark this PHI as
       // replacable and push it's users into the worklist.
-      bool IsReplaceable = true;
-      if (all_of(PHI->incoming_values(), [&](Value *V) {
-            if (!isa<Instruction>(V))
-              return IsReplaceable = false;
-            return isAvailable(cast<Instruction>(V));
-          })) {
+      bool IsReplaceable = all_of(PHI->incoming_values(), [](Value *V) {
+        return isa<Instruction>(V);
+      });
+      if (IsReplaceable && all_of(PHI->incoming_values(), [&](Value *V) {
+        return isAvailable(cast<Instruction>(V));
+      })) {
         UsersToReplace.insert(PHI);
         PushUsersToWorklist(PHI);
         continue;

[gandhi56]

@milos1397 Could you please reduce and attach the test case? The change seems fine to me.