[llvm] [InstCombine] Set `samesign` when converting signed predicates into unsigned (PR #112642)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

Alive2: https://alive2.llvm.org/ce/z/6cqdt-


---
Full diff: https://github.com/llvm/llvm-project/pull/112642.diff


5 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+5-2) 
- (modified) llvm/test/Transforms/InstCombine/call-guard.ll (+1-1) 
- (modified) llvm/test/Transforms/InstCombine/icmp.ll (+1-1) 
- (modified) llvm/test/Transforms/InstCombine/indexed-gep-compares.ll (+1-1) 
- (modified) llvm/test/Transforms/InstCombine/phi-known-bits-operand-order.ll (+2-2) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 18a6fdcec1728e..a9c88444ba2571 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6774,8 +6774,11 @@ Instruction *InstCombinerImpl::foldICmpUsingKnownBits(ICmpInst &I) {
   // have the same sign.
   if (I.isSigned() &&
       ((Op0Known.Zero.isNegative() && Op1Known.Zero.isNegative()) ||
-       (Op0Known.One.isNegative() && Op1Known.One.isNegative())))
-    return new ICmpInst(I.getUnsignedPredicate(), Op0, Op1);
+       (Op0Known.One.isNegative() && Op1Known.One.isNegative()))) {
+    ICmpInst *NewICmp = new ICmpInst(I.getUnsignedPredicate(), Op0, Op1);
+    NewICmp->setSameSign();
+    return NewICmp;
+  }
 
   return nullptr;
 }
diff --git a/llvm/test/Transforms/InstCombine/call-guard.ll b/llvm/test/Transforms/InstCombine/call-guard.ll
index 6b31c78118d0b8..bc5f319e64f7fe 100644
--- a/llvm/test/Transforms/InstCombine/call-guard.ll
+++ b/llvm/test/Transforms/InstCombine/call-guard.ll
@@ -43,7 +43,7 @@ define void @test_guard_adjacent_diff_cond2(i32 %V1, i32 %V2) {
 ; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[V1:%.*]], [[V2:%.*]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = icmp slt i32 [[TMP1]], 0
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[V1]], 255
-; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[AND]], 129
+; CHECK-NEXT:    [[C:%.*]] = icmp samesign ult i32 [[AND]], 129
 ; CHECK-NEXT:    [[TMP3:%.*]] = and i1 [[TMP2]], [[C]]
 ; CHECK-NEXT:    call void (i1, ...) @llvm.experimental.guard(i1 [[TMP3]], i32 123) [ "deopt"() ]
 ; CHECK-NEXT:    ret void
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 7cafb4885ff0ee..e44f7002438cb9 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -1457,7 +1457,7 @@ define <2 x i1> @test67vecinverse(<2 x i32> %x) {
 define i1 @test68(i32 %x) {
 ; CHECK-LABEL: @test68(
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[X:%.*]], 127
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[AND]], 30
+; CHECK-NEXT:    [[CMP:%.*]] = icmp samesign ugt i32 [[AND]], 30
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %and = and i32 %x, 127
diff --git a/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll b/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
index 79511cf9e666ff..1110bbc5403e49 100644
--- a/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
+++ b/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
@@ -40,7 +40,7 @@ define ptr @test1_nuw(ptr %A, i32 %Offset) {
 ; CHECK:       bb:
 ; CHECK-NEXT:    [[RHS_IDX:%.*]] = phi i32 [ [[RHS_ADD:%.*]], [[BB]] ], [ [[TMP_IDX]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[RHS_ADD]] = add nuw nsw i32 [[RHS_IDX]], 4
-; CHECK-NEXT:    [[COND:%.*]] = icmp ugt i32 [[RHS_IDX]], 400
+; CHECK-NEXT:    [[COND:%.*]] = icmp samesign ugt i32 [[RHS_IDX]], 400
 ; CHECK-NEXT:    br i1 [[COND]], label [[BB2:%.*]], label [[BB]]
 ; CHECK:       bb2:
 ; CHECK-NEXT:    [[RHS_PTR:%.*]] = getelementptr inbounds nuw i8, ptr [[A:%.*]], i32 [[RHS_IDX]]
diff --git a/llvm/test/Transforms/InstCombine/phi-known-bits-operand-order.ll b/llvm/test/Transforms/InstCombine/phi-known-bits-operand-order.ll
index 6a054688753500..9ff093635ad793 100644
--- a/llvm/test/Transforms/InstCombine/phi-known-bits-operand-order.ll
+++ b/llvm/test/Transforms/InstCombine/phi-known-bits-operand-order.ll
@@ -20,7 +20,7 @@ define void @phi_recurrence_start_first() {
 ; CHECK-NEXT:    br i1 [[COND_V2]], label [[FOR_COND11:%.*]], label [[FOR_COND26]]
 ; CHECK:       for.cond11:
 ; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[START]], [[IF_THEN]] ], [ [[STEP:%.*]], [[FOR_COND11]] ]
-; CHECK-NEXT:    [[CMP13:%.*]] = icmp ult i32 [[I_1]], 100
+; CHECK-NEXT:    [[CMP13:%.*]] = icmp samesign ult i32 [[I_1]], 100
 ; CHECK-NEXT:    [[STEP]] = add nuw nsw i32 [[I_1]], 1
 ; CHECK-NEXT:    br i1 [[CMP13]], label [[FOR_COND11]], label [[WHILE_END]]
 ; CHECK:       for.cond26:
@@ -68,7 +68,7 @@ define void @phi_recurrence_step_first() {
 ; CHECK-NEXT:    br i1 [[COND_V2]], label [[FOR_COND11:%.*]], label [[FOR_COND26]]
 ; CHECK:       for.cond11:
 ; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[STEP:%.*]], [[FOR_COND11]] ], [ [[START]], [[IF_THEN]] ]
-; CHECK-NEXT:    [[CMP13:%.*]] = icmp ult i32 [[I_1]], 100
+; CHECK-NEXT:    [[CMP13:%.*]] = icmp samesign ult i32 [[I_1]], 100
 ; CHECK-NEXT:    [[STEP]] = add nuw nsw i32 [[I_1]], 1
 ; CHECK-NEXT:    br i1 [[CMP13]], label [[FOR_COND11]], label [[WHILE_END]]
 ; CHECK:       for.cond26:

``````````

</details>


https://github.com/llvm/llvm-project/pull/112642