[llvm] [InstCombine] Avoid crash on aggregate types in SimplifyDemandedUseFPClass (PR #111128)

[Benjamin Maxwell via llvm-commits]

https://github.com/MacDue created https://github.com/llvm/llvm-project/pull/111128

The disables folding to FP aggregates that are not poison types, which is currently not supported. Note: To fully handle this case would also likely require teaching `computeKnownFPClass()` to handle array and struct constants (which does not seem implemented outside of zero init).

>From d92961a7c80807b3e706a9ef552a68ff11f3e41a Mon Sep 17 00:00:00 2001
From: Benjamin Maxwell <benjamin.maxwell at arm.com>
Date: Fri, 4 Oct 2024 10:14:37 +0000
Subject: [PATCH] [InstCombine] Avoid crash on aggregate types in
 SimplifyDemandedUseFPClass

The disables folding to FP aggregates that are not poison types, which
is currently not supported. Note: To fully handle this case would also
likely require teaching `computeKnownFPClass()` to handle array and
struct constants (which does not seem implemented outside of zero init).
---
 .../InstCombineSimplifyDemanded.cpp           | 13 +++++++++
 .../InstCombine/simplify-demanded-fpclass.ll  | 29 +++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index ee6b60f7f70d68..cb8c0dff7ba7dd 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1919,6 +1919,19 @@ Value *InstCombinerImpl::SimplifyDemandedVectorElts(Value *V,
 /// For floating-point classes that resolve to a single bit pattern, return that
 /// value.
 static Constant *getFPClassConstant(Type *Ty, FPClassTest Mask) {
+  // TODO: Support aggregate types that are allowed by FPMathOperator.
+  switch (Mask) {
+    case fcPosZero:
+    case fcNegZero:
+    case fcPosInf:
+    case fcNegInf:
+      if (Ty->isAggregateType())
+        return nullptr;
+      break;
+    default:
+      break;
+  }
+
   switch (Mask) {
   case fcPosZero:
     return ConstantFP::getZero(Ty);
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
index 403f3bacf34d89..c03c31f4f41ba7 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -91,6 +91,35 @@ define nofpclass(inf) float @ret_nofpclass_inf__ninf() {
   ret float 0xFFF0000000000000
 }
 
+; Basic aggregate tests to ensure this does not crash.
+define nofpclass(nan) { float } @ret_nofpclass_struct_ty() {
+; CHECK-LABEL: define nofpclass(nan) { float } @ret_nofpclass_struct_ty() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret { float } zeroinitializer
+;
+entry:
+  ret { float } zeroinitializer
+}
+
+
+define nofpclass(nan) [ 5 x float ] @ret_nofpclass_array_ty() {
+; CHECK-LABEL: define nofpclass(nan) [5 x float] @ret_nofpclass_array_ty() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret [5 x float] zeroinitializer
+;
+entry:
+  ret [ 5 x float ] zeroinitializer
+}
+
+define nofpclass(nan) [ 2 x [ 5 x float ]] @ret_nofpclass_nested_array_ty() {
+; CHECK-LABEL: define nofpclass(nan) [2 x [5 x float]] @ret_nofpclass_nested_array_ty() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret [2 x [5 x float]] zeroinitializer
+;
+entry:
+  ret [ 2 x [ 5 x float ]] zeroinitializer
+}
+
 ; Negative test, do nothing
 define nofpclass(inf) float @ret_nofpclass_inf__select_nofpclass_inf_lhs(i1 %cond, float nofpclass(inf) %x, float %y) {
 ; CHECK-LABEL: define nofpclass(inf) float @ret_nofpclass_inf__select_nofpclass_inf_lhs