[llvm] d3dad7a - [InstCombine] Fix miscompilation caused by #90436 (#91133)

[via llvm-commits]

Author: Yingwei Zheng
Date: 2024-05-06T16:30:07+08:00
New Revision: d3dad7a74be50d90754bf5c072e1a2330e92712c

URL: https://github.com/llvm/llvm-project/commit/d3dad7a74be50d90754bf5c072e1a2330e92712c
DIFF: https://github.com/llvm/llvm-project/commit/d3dad7a74be50d90754bf5c072e1a2330e92712c.diff

LOG: [InstCombine] Fix miscompilation caused by #90436 (#91133)

Proof: https://alive2.llvm.org/ce/z/iRnJ4i

Fixes https://github.com/llvm/llvm-project/issues/91127.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index c60a290ce72e06..7092fb5e509bb1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1510,6 +1510,7 @@ InstCombinerImpl::foldICmpTruncWithTruncOrExt(ICmpInst &Cmp,
       std::swap(X, Y);
       Pred = Cmp.getSwappedPredicate(Pred);
     }
+    YIsSExt = !(NoWrapFlags & TruncInst::NoUnsignedWrap);
   }
   // Try to match icmp (trunc nuw X), (zext Y)
   else if (!Cmp.isSigned() &&

diff  --git a/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll b/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll
index 0a8bf013dc55d2..a1757fbb84b231 100644
--- a/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll
@@ -568,3 +568,77 @@ define i1 @trunc_equality_both_sext(i32 %x, i8 %y) {
   %c = icmp ne i16 %xt, %ye
   ret i1 %c
 }
+
+define i1 @test_eq1(i32 %x, i16 %y) {
+; CHECK-LABEL: @test_eq1(
+; CHECK-NEXT:    [[TMP1:%.*]] = sext i16 [[Y:%.*]] to i32
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %conv1 = trunc nsw i32 %x to i8
+  %conv2 = trunc nsw i16 %y to i8
+  %cond = icmp eq i8 %conv1, %conv2
+  ret i1 %cond
+}
+
+; FIXME: It is weird that we generate truncs for test_eq2, but not for test_eq1.
+
+define i1 @test_eq2(i32 %x, i16 %y) {
+; CHECK-LABEL: @test_eq2(
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[X:%.*]] to i16
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i16 [[TMP1]], [[Y:%.*]]
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %conv1 = trunc nsw i32 %x to i8
+  %conv2 = trunc nsw i16 %y to i8
+  %cond = icmp eq i8 %conv2, %conv1
+  ret i1 %cond
+}
+
+define i1 @test_ult(i32 %x, i16 %y) {
+; CHECK-LABEL: @test_ult(
+; CHECK-NEXT:    [[TMP1:%.*]] = sext i16 [[Y:%.*]] to i32
+; CHECK-NEXT:    [[COND:%.*]] = icmp ugt i32 [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %conv1 = trunc nsw i32 %x to i8
+  %conv2 = trunc nsw i16 %y to i8
+  %cond = icmp ult i8 %conv1, %conv2
+  ret i1 %cond
+}
+
+define i1 @test_slt(i32 %x, i16 %y) {
+; CHECK-LABEL: @test_slt(
+; CHECK-NEXT:    [[TMP1:%.*]] = sext i16 [[Y:%.*]] to i32
+; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %conv1 = trunc nsw i32 %x to i8
+  %conv2 = trunc nsw i16 %y to i8
+  %cond = icmp slt i8 %conv1, %conv2
+  ret i1 %cond
+}
+
+define i1 @test_ult_nuw(i32 %x, i16 %y) {
+; CHECK-LABEL: @test_ult_nuw(
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i16 [[Y:%.*]] to i32
+; CHECK-NEXT:    [[COND:%.*]] = icmp ugt i32 [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %conv1 = trunc nuw nsw i32 %x to i8
+  %conv2 = trunc nuw nsw i16 %y to i8
+  %cond = icmp ult i8 %conv1, %conv2
+  ret i1 %cond
+}
+
+define i1 @test_slt_nuw(i32 %x, i16 %y) {
+; CHECK-LABEL: @test_slt_nuw(
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i16 [[Y:%.*]] to i32
+; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %conv1 = trunc nuw nsw i32 %x to i8
+  %conv2 = trunc nuw nsw i16 %y to i8
+  %cond = icmp slt i8 %conv1, %conv2
+  ret i1 %cond
+}