Fix pattern match for umin(UINT_MAX, BinOp(zext(A), zext(B))).

Bail out if BinOp is not known non-negative.
llvm · Jul 17, 2024 · 603655d · 603655d
1 parent 5010937
commit 603655d
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Showing 2 changed files with 27 additions and 6 deletions.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1141,6 +1141,9 @@ Instruction *InstCombinerImpl::matchAddSubSat(IntrinsicInst &MinMax1) {
     if (!match(MinMax2, m_SMin(m_BinOp(AddSub), m_APInt(MaxValue))))
       return nullptr;
   } else if (match(&MinMax1, m_UMin(m_BinOp(AddSub), m_APInt(MaxValue)))) {
+    // Bail out if AddSub could be negative.
+    if (!isKnownNonNegative(AddSub, SQ.getWithInstruction(AddSub)))
+      return nullptr;
     IsUnsignedSaturate = true;
   } else
     return nullptr;

diff --git a/llvm/test/Transforms/InstCombine/uaddsub_sat.ll b/llvm/test/Transforms/InstCombine/uaddsub_sat.ll
@@ -218,12 +218,12 @@ define i64 @uadd_sat64(i64 %a, i64 %b) {
 ; CHECK-NEXT:    ret i64 [[TMP0]]
 ;
 entry:
-  %conv = zext i64 %a to i65
-  %conv1 = zext i64 %b to i65
-  %add = add i65 %conv1, %conv
-  %0 = icmp ult i65 %add, 18446744073709551615
-  %select = select i1 %0, i65 %add, i65 18446744073709551615
-  %conv2 = trunc i65 %select to i64
+  %conv = zext i64 %a to i128
+  %conv1 = zext i64 %b to i128
+  %add = add i128 %conv1, %conv
+  %0 = icmp ult i128 %add, 18446744073709551615
+  %select = select i1 %0, i128 %add, i128 18446744073709551615
+  %conv2 = trunc i128 %select to i64
   ret i64 %conv2
 }
 
@@ -487,6 +487,24 @@ define i8 @const(i8 %X) {
   ret i8 %conv
 }
 
+define i32 @invalid_sub_could_be_negative(i32 %a, i32 %b) {
+; CHECK-LABEL: define i32 @invalid_sub_could_be_negative(
+; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:    [[CONV:%.*]] = zext i32 [[A]] to i64
+; CHECK-NEXT:    [[CONV3:%.*]] = zext i32 [[B]] to i64
+; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i64 [[CONV]], [[CONV3]]
+; CHECK-NEXT:    [[SPEC_STORE_SELECT13:%.*]] = call i64 @llvm.umin.i64(i64 [[SUB]], i64 4294967295)
+; CHECK-NEXT:    [[CONV10:%.*]] = trunc nuw i64 [[SPEC_STORE_SELECT13]] to i32
+; CHECK-NEXT:    ret i32 [[CONV10]]
+;
+  %conv = zext i32 %a to i64
+  %conv3 = zext i32 %b to i64
+  %sub = sub nsw i64 %conv, %conv3
+  %spec.store.select13 = call i64 @llvm.umin.i64(i64 %sub, i64 4294967295)
+  %conv10 = trunc i64 %spec.store.select13 to i32
+  ret i32 %conv10
+}
+
 declare void @use64(i64)
 declare i64 @llvm.umin.i64(i64, i64)
 declare i64 @llvm.smin.i64(i64, i64)