[llvm-branch-commits] [llvm] release/21.x: [SelectOptimize] Fix incorrect -1 immediate for large integers (#170860) (PR #171596)

[via llvm-branch-commits]

https://github.com/dyung updated https://github.com/llvm/llvm-project/pull/171596

>From d2e835bd46384aa1628c9d44e3f93438f0795dfd Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 10 Dec 2025 11:31:07 +0100
Subject: [PATCH] [SelectOptimize] Fix incorrect -1 immediate for large
 integers (#170860)

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

(cherry picked from commit 1165e41c876f3beba938805329416647bd21ee5e)
---
 llvm/lib/CodeGen/SelectOptimize.cpp         |  2 +-
 llvm/test/CodeGen/AArch64/selectopt-cast.ll | 46 +++++++++++++++++++++
 2 files changed, 47 insertions(+), 1 deletion(-)

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..47cc736ad6880 100644
--- a/llvm/test/CodeGen/AArch64/selectopt-cast.ll
+++ b/llvm/test/CodeGen/AArch64/selectopt-cast.ll
@@ -901,3 +901,49 @@ loop:
 exit:
   ret void
 }
+
+define void @sext_i128() {
+; CHECK-LABEL: @sext_i128(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[I:%.*]] = icmp slt i128 0, 0
+; CHECK-NEXT:    [[I2:%.*]] = sext i1 [[I]] to i128
+; CHECK-NEXT:    [[I3:%.*]] = or i128 [[I2]], 0
+; CHECK-NEXT:    [[I4:%.*]] = icmp slt i128 [[I3]], 0
+; CHECK-NEXT:    [[I5:%.*]] = sext i1 [[I4]] to i128
+; CHECK-NEXT:    [[I4_FROZEN:%.*]] = freeze i1 [[I4]]
+; CHECK-NEXT:    br i1 [[I4_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:    [[I6:%.*]] = phi i128 [ [[TMP0]], [[SELECT_TRUE_SINK]] ], [ 0, [[LOOP]] ]
+; CHECK-NEXT:    [[I7:%.*]] = icmp slt i128 [[I6]], 0
+; CHECK-NEXT:    [[I8:%.*]] = sext i1 [[I7]] to i128
+; CHECK-NEXT:    [[I7_FROZEN:%.*]] = freeze i1 [[I7]]
+; CHECK-NEXT:    br i1 [[I7_FROZEN]], label [[SELECT_TRUE_SINK2:%.*]], label [[SELECT_END1:%.*]]
+; CHECK:       select.true.sink2:
+; CHECK-NEXT:    [[TMP1:%.*]] = add i128 -1, 0
+; CHECK-NEXT:    br label [[SELECT_END1]]
+; CHECK:       select.end1:
+; CHECK-NEXT:    [[I9:%.*]] = phi i128 [ [[TMP1]], [[SELECT_TRUE_SINK2]] ], [ 0, [[SELECT_END]] ]
+; CHECK-NEXT:    [[I10:%.*]] = or i128 [[I9]], 0
+; CHECK-NEXT:    br label [[LOOP]]
+;
+entry:
+  br label %loop
+
+loop:
+  %i = icmp slt i128 0, 0
+  %i2 = sext i1 %i to i128
+  %i3 = or i128 %i2, 0
+  %i4 = icmp slt i128 %i3, 0
+  %i5 = sext i1 %i4 to i128
+  %i6 = add i128 %i5, 0
+  %i7 = icmp slt i128 %i6, 0
+  %i8 = sext i1 %i7 to i128
+  %i9 = add i128 %i8, 0
+  %i10 = or i128 %i9, 0
+  br label %loop
+}