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

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

Fixes #91127.

Author: dtcxzyw

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() &&

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
+}