[llvm] aa6d541 - [InstSimplify] Fold {u,s}{min,max} x, poison -> poison (#138166)

[via llvm-commits]

Author: Luke Lau
Date: 2025-05-02T07:49:27+08:00
New Revision: aa6d541065ef755bea9c6ed2b3598f0664c10002

URL: https://github.com/llvm/llvm-project/commit/aa6d541065ef755bea9c6ed2b3598f0664c10002
DIFF: https://github.com/llvm/llvm-project/commit/aa6d541065ef755bea9c6ed2b3598f0664c10002.diff

LOG: [InstSimplify] Fold {u,s}{min,max} x, poison -> poison (#138166)

Following from the discussion in
https://github.com/llvm/llvm-project/pull/138095#discussion_r2070484664,
these intrinsics are poison if any of their operands are poison, and are
marked as such in propagatesPoison in ValueTracking.cpp.

This will help fold away leftover vectors produced by VectorCombine when
scalarizing intrinsics.

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstSimplify/maxmin_intrinsics.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 718d272dd0ac7..5a2943de9066e 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -6541,6 +6541,10 @@ Value *llvm::simplifyBinaryIntrinsic(Intrinsic::ID IID, Type *ReturnType,
     if (match(Op0, m_ImmConstant()))
       std::swap(Op0, Op1);
 
+    // Propagate poison.
+    if (isa<PoisonValue>(Op1))
+      return Op1;
+
     // Assume undef is the limit value.
     if (Q.isUndefValue(Op1))
       return ConstantInt::get(

diff  --git a/llvm/test/Transforms/InstSimplify/maxmin_intrinsics.ll b/llvm/test/Transforms/InstSimplify/maxmin_intrinsics.ll
index ddd4140b3aedd..98bfe5329c290 100644
--- a/llvm/test/Transforms/InstSimplify/maxmin_intrinsics.ll
+++ b/llvm/test/Transforms/InstSimplify/maxmin_intrinsics.ll
@@ -75,7 +75,7 @@ define i81 @smax_undef(i81 %x) {
 
 define i81 @smax_poison(i81 %x) {
 ; CHECK-LABEL: @smax_poison(
-; CHECK-NEXT:    ret i81 1208925819614629174706175
+; CHECK-NEXT:    ret i81 poison
 ;
   %r = call i81 @llvm.smax.i81(i81 poison, i81 %x)
   ret i81 %r
@@ -91,7 +91,7 @@ define i3 @smin_undef(i3 %x) {
 
 define i3 @smin_poison(i3 %x) {
 ; CHECK-LABEL: @smin_poison(
-; CHECK-NEXT:    ret i3 -4
+; CHECK-NEXT:    ret i3 poison
 ;
   %r = call i3 @llvm.smin.i3(i3 %x, i3 poison)
   ret i3 %r
@@ -107,7 +107,7 @@ define <2 x i8> @umax_undef(<2 x i8> %x) {
 
 define <2 x i8> @umax_poison(<2 x i8> %x) {
 ; CHECK-LABEL: @umax_poison(
-; CHECK-NEXT:    ret <2 x i8> splat (i8 -1)
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %r = call <2 x i8> @llvm.umax.v2i8(<2 x i8> poison, <2 x i8> %x)
   ret <2 x i8> %r
@@ -123,7 +123,7 @@ define <2 x i8> @umin_undef(<2 x i8> %x) {
 
 define <2 x i8> @umin_poison(<2 x i8> %x) {
 ; CHECK-LABEL: @umin_poison(
-; CHECK-NEXT:    ret <2 x i8> zeroinitializer
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %r = call <2 x i8> @llvm.umin.v2i8(<2 x i8> %x, <2 x i8> poison)
   ret <2 x i8> %r