[llvm] 1165e41 - [SelectOptimize] Fix incorrect -1 immediate for large integers (#170860)

[via llvm-commits]

Author: Nikita Popov
Date: 2025-12-10T11:31:07+01:00
New Revision: 1165e41c876f3beba938805329416647bd21ee5e

URL: https://github.com/llvm/llvm-project/commit/1165e41c876f3beba938805329416647bd21ee5e
DIFF: https://github.com/llvm/llvm-project/commit/1165e41c876f3beba938805329416647bd21ee5e.diff

LOG: [SelectOptimize] Fix incorrect -1 immediate for large integers (#170860)

This was creating a -1 with zero extension, while it needs to use sign
extension.

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectOptimize.cpp
    llvm/test/CodeGen/AArch64/selectopt-cast.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectOptimize.cpp b/llvm/lib/CodeGen/SelectOptimize.cpp
index 13ed8f28d5507..2052e9a75d89b 100644
--- a/llvm/lib/CodeGen/SelectOptimize.cpp
+++ b/llvm/lib/CodeGen/SelectOptimize.cpp
@@ -502,7 +502,7 @@ static Value *getTrueOrFalseValue(
   } else {
     assert((isa<AShrOperator>(AuxI) || isa<SExtInst>(AuxI)) &&
            "Unexpected opcode");
-    CBO->setOperand(CondIdx, ConstantInt::get(CBO->getType(), -1));
+    CBO->setOperand(CondIdx, ConstantInt::getAllOnesValue(CBO->getType()));
   }
 
   unsigned OtherIdx = 1 - CondIdx;

diff  --git a/llvm/test/CodeGen/AArch64/selectopt-cast.ll b/llvm/test/CodeGen/AArch64/selectopt-cast.ll
index b862458e99fe2..e363cb369286e 100644
--- a/llvm/test/CodeGen/AArch64/selectopt-cast.ll
+++ b/llvm/test/CodeGen/AArch64/selectopt-cast.ll
@@ -901,3 +901,40 @@ loop:
 exit:
   ret void
 }
+
+declare void @use(i128)
+
+define void @sext_i128(ptr %a) {
+; CHECK-LABEL: @sext_i128(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[LOAD:%.*]] = load i128, ptr [[A:%.*]], align 16
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i128 [[LOAD]], 0
+; CHECK-NEXT:    [[SEXT1:%.*]] = sext i1 [[CMP1]] to i128
+; CHECK-NEXT:    [[CMP1_FROZEN:%.*]] = freeze i1 [[CMP1]]
+; CHECK-NEXT:    br i1 [[CMP1_FROZEN]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_END:%.*]]
+; CHECK:       select.true.sink:
+; CHECK-NEXT:    [[TMP0:%.*]] = add i128 -1, 0
+; CHECK-NEXT:    br label [[SELECT_END]]
+; CHECK:       select.end:
+; CHECK-NEXT:    [[ADD:%.*]] = phi i128 [ [[TMP0]], [[SELECT_TRUE_SINK]] ], [ 0, [[LOOP]] ]
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i128 [[ADD]], 0
+; CHECK-NEXT:    br i1 [[CMP2]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  %load = load i128, ptr %a, align 16
+  %cmp1 = icmp slt i128 %load, 0
+  %sext1 = sext i1 %cmp1 to i128
+  %add = add i128 %sext1, 0
+  %cmp2 = icmp slt i128 %add, 0
+  br i1 %cmp2, label %loop, label %exit
+
+exit:
+  ret void
+}