[CGExprScalar] Fix inc/dec of vector larger than 64-bit #172301
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Use getSigned() to create the 1 or -1 constant, so it gets properly sign extended.
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@llvm/pr-subscribers-clang-codegen @llvm/pr-subscribers-backend-systemz Author: Nikita Popov (nikic) ChangesUse getSigned() to create the 1 or -1 constant, so it gets properly sign extended. This miscompile was found while working on #171456. Full diff: https://github.com/llvm/llvm-project/pull/172301.diff 2 Files Affected:
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 769bc37b0e131..9b6497fca829a 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -3335,7 +3335,7 @@ ScalarExprEmitter::EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
// Vector increment/decrement.
} else if (type->isVectorType()) {
if (type->hasIntegerRepresentation()) {
- llvm::Value *amt = llvm::ConstantInt::get(value->getType(), amount);
+ llvm::Value *amt = llvm::ConstantInt::getSigned(value->getType(), amount);
value = Builder.CreateAdd(value, amt, isInc ? "inc" : "dec");
} else {
diff --git a/clang/test/CodeGen/SystemZ/zvector.c b/clang/test/CodeGen/SystemZ/zvector.c
index a0b654d9acc9a..35bee8d41df61 100644
--- a/clang/test/CodeGen/SystemZ/zvector.c
+++ b/clang/test/CodeGen/SystemZ/zvector.c
@@ -298,10 +298,10 @@ void test_postinc(void) {
// CHECK-NEXT: [[DEC7:%.*]] = add <2 x i64> [[TMP7]], splat (i64 -1)
// CHECK-NEXT: store volatile <2 x i64> [[DEC7]], ptr @ul2, align 8
// CHECK-NEXT: [[TMP8:%.*]] = load volatile <1 x i128>, ptr @slll2, align 8
-// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC8]], ptr @slll2, align 8
// CHECK-NEXT: [[TMP9:%.*]] = load volatile <1 x i128>, ptr @ulll2, align 8
-// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC9]], ptr @ulll2, align 8
// CHECK-NEXT: [[TMP10:%.*]] = load volatile <2 x double>, ptr @fd2, align 8
// CHECK-NEXT: [[DEC10:%.*]] = fadd <2 x double> [[TMP10]], splat (double -1.000000e+00)
@@ -356,10 +356,10 @@ void test_predec(void) {
// CHECK-NEXT: [[DEC7:%.*]] = add <2 x i64> [[TMP7]], splat (i64 -1)
// CHECK-NEXT: store volatile <2 x i64> [[DEC7]], ptr @ul2, align 8
// CHECK-NEXT: [[TMP8:%.*]] = load volatile <1 x i128>, ptr @slll2, align 8
-// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC8]], ptr @slll2, align 8
// CHECK-NEXT: [[TMP9:%.*]] = load volatile <1 x i128>, ptr @ulll2, align 8
-// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC9]], ptr @ulll2, align 8
// CHECK-NEXT: [[TMP10:%.*]] = load volatile <2 x double>, ptr @fd2, align 8
// CHECK-NEXT: [[DEC10:%.*]] = fadd <2 x double> [[TMP10]], splat (double -1.000000e+00)
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Member
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@llvm/pr-subscribers-clang Author: Nikita Popov (nikic) ChangesUse getSigned() to create the 1 or -1 constant, so it gets properly sign extended. This miscompile was found while working on #171456. Full diff: https://github.com/llvm/llvm-project/pull/172301.diff 2 Files Affected:
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 769bc37b0e131..9b6497fca829a 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -3335,7 +3335,7 @@ ScalarExprEmitter::EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
// Vector increment/decrement.
} else if (type->isVectorType()) {
if (type->hasIntegerRepresentation()) {
- llvm::Value *amt = llvm::ConstantInt::get(value->getType(), amount);
+ llvm::Value *amt = llvm::ConstantInt::getSigned(value->getType(), amount);
value = Builder.CreateAdd(value, amt, isInc ? "inc" : "dec");
} else {
diff --git a/clang/test/CodeGen/SystemZ/zvector.c b/clang/test/CodeGen/SystemZ/zvector.c
index a0b654d9acc9a..35bee8d41df61 100644
--- a/clang/test/CodeGen/SystemZ/zvector.c
+++ b/clang/test/CodeGen/SystemZ/zvector.c
@@ -298,10 +298,10 @@ void test_postinc(void) {
// CHECK-NEXT: [[DEC7:%.*]] = add <2 x i64> [[TMP7]], splat (i64 -1)
// CHECK-NEXT: store volatile <2 x i64> [[DEC7]], ptr @ul2, align 8
// CHECK-NEXT: [[TMP8:%.*]] = load volatile <1 x i128>, ptr @slll2, align 8
-// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC8]], ptr @slll2, align 8
// CHECK-NEXT: [[TMP9:%.*]] = load volatile <1 x i128>, ptr @ulll2, align 8
-// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC9]], ptr @ulll2, align 8
// CHECK-NEXT: [[TMP10:%.*]] = load volatile <2 x double>, ptr @fd2, align 8
// CHECK-NEXT: [[DEC10:%.*]] = fadd <2 x double> [[TMP10]], splat (double -1.000000e+00)
@@ -356,10 +356,10 @@ void test_predec(void) {
// CHECK-NEXT: [[DEC7:%.*]] = add <2 x i64> [[TMP7]], splat (i64 -1)
// CHECK-NEXT: store volatile <2 x i64> [[DEC7]], ptr @ul2, align 8
// CHECK-NEXT: [[TMP8:%.*]] = load volatile <1 x i128>, ptr @slll2, align 8
-// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC8:%.*]] = add <1 x i128> [[TMP8]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC8]], ptr @slll2, align 8
// CHECK-NEXT: [[TMP9:%.*]] = load volatile <1 x i128>, ptr @ulll2, align 8
-// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 18446744073709551615)
+// CHECK-NEXT: [[DEC9:%.*]] = add <1 x i128> [[TMP9]], splat (i128 -1)
// CHECK-NEXT: store volatile <1 x i128> [[DEC9]], ptr @ulll2, align 8
// CHECK-NEXT: [[TMP10:%.*]] = load volatile <2 x double>, ptr @fd2, align 8
// CHECK-NEXT: [[DEC10:%.*]] = fadd <2 x double> [[TMP10]], splat (double -1.000000e+00)
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uweigand
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Dec 15, 2025
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SystemZ change looks good to me, that fixes an actual bug. Thanks!
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Use getSigned() to create the 1 or -1 constant, so it gets properly sign extended.
This miscompile was found while working on #171456.