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

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,82 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+define i1 @test_eq1(i32 %x, i16 %y) {
+; CHECK-LABEL: define i1 @test_eq1(
+; CHECK-SAME: i32 [[X:%.*]], i16 [[Y:%.*]]) {
+; 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: define i1 @test_eq2(
+; CHECK-SAME: i32 [[X:%.*]], i16 [[Y:%.*]]) {
+; 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: define i1 @test_ult(
+; CHECK-SAME: i32 [[X:%.*]], i16 [[Y:%.*]]) {
+; 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: define i1 @test_slt(
+; CHECK-SAME: i32 [[X:%.*]], i16 [[Y:%.*]]) {
+; 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: define i1 @test_ult_nuw(
+; CHECK-SAME: i32 [[X:%.*]], i16 [[Y:%.*]]) {
+; 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: define i1 @test_slt_nuw(
+; CHECK-SAME: i32 [[X:%.*]], i16 [[Y:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i16 [[Y]] to i32
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nikic wrote:

We could also add nneg in these cases.

https://github.com/llvm/llvm-project/pull/91133