[llvm] 6e379de - [Reassociate] Preserve `nuw` and `nsw` on `mul` chains
Noah Goldstein via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 1 07:23:02 PDT 2024
Author: Noah Goldstein
Date: 2024-07-01T22:22:36+08:00
New Revision: 6e379de3b144363c2f5a6f9335eef6f42e28ef37
URL: https://github.com/llvm/llvm-project/commit/6e379de3b144363c2f5a6f9335eef6f42e28ef37
DIFF: https://github.com/llvm/llvm-project/commit/6e379de3b144363c2f5a6f9335eef6f42e28ef37.diff
LOG: [Reassociate] Preserve `nuw` and `nsw` on `mul` chains
Basically the same rules as `add` but we also need to ensure all
operands a non-zero.
Proofs: https://alive2.llvm.org/ce/z/jzsYht
Closes #97040
Added:
Modified:
llvm/include/llvm/Transforms/Scalar/Reassociate.h
llvm/lib/Transforms/Scalar/Reassociate.cpp
llvm/test/Transforms/Reassociate/reassoc-mul-nuw.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/Transforms/Scalar/Reassociate.h b/llvm/include/llvm/Transforms/Scalar/Reassociate.h
index 8c93afcd587e8..3b2d2b83ced62 100644
--- a/llvm/include/llvm/Transforms/Scalar/Reassociate.h
+++ b/llvm/include/llvm/Transforms/Scalar/Reassociate.h
@@ -68,10 +68,13 @@ struct OverflowTracking {
bool HasNUW;
bool HasNSW;
bool AllKnownNonNegative;
+ bool AllKnownNonZero;
// Note: AllKnownNonNegative can be true in a case where one of the operands
// is negative, but one the operators is not NSW. AllKnownNonNegative should
// not be used independently of HasNSW
- OverflowTracking() : HasNUW(true), HasNSW(true), AllKnownNonNegative(true) {}
+ OverflowTracking()
+ : HasNUW(true), HasNSW(true), AllKnownNonNegative(true),
+ AllKnownNonZero(true) {}
};
class XorOpnd;
diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index ce7b95af24291..cc01d2e59a87e 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -539,6 +539,16 @@ static bool LinearizeExprTree(Instruction *I,
Ops.push_back(std::make_pair(V, Weight));
if (Opcode == Instruction::Add && Flags.AllKnownNonNegative && Flags.HasNSW)
Flags.AllKnownNonNegative &= isKnownNonNegative(V, SimplifyQuery(DL));
+ else if (Opcode == Instruction::Mul) {
+ // To preserve NUW we need all inputs non-zero.
+ // To preserve NSW we need all inputs strictly positive.
+ if (Flags.AllKnownNonZero &&
+ (Flags.HasNUW || (Flags.HasNSW && Flags.AllKnownNonNegative))) {
+ Flags.AllKnownNonZero &= isKnownNonZero(V, SimplifyQuery(DL));
+ if (Flags.HasNSW && Flags.AllKnownNonNegative)
+ Flags.AllKnownNonNegative &= isKnownNonNegative(V, SimplifyQuery(DL));
+ }
+ }
}
// For nilpotent operations or addition there may be no operands, for example
@@ -722,10 +732,9 @@ void ReassociatePass::RewriteExprTree(BinaryOperator *I,
ExpressionChangedStart->setFastMathFlags(Flags);
} else {
ExpressionChangedStart->clearSubclassOptionalData();
- // Note that it doesn't hold for mul if one of the operands is zero.
- // TODO: We can preserve NUW flag if we prove that all mul operands
- // are non-zero.
- if (ExpressionChangedStart->getOpcode() == Instruction::Add) {
+ if (ExpressionChangedStart->getOpcode() == Instruction::Add ||
+ (ExpressionChangedStart->getOpcode() == Instruction::Mul &&
+ Flags.AllKnownNonZero)) {
if (Flags.HasNUW)
ExpressionChangedStart->setHasNoUnsignedWrap();
if (Flags.HasNSW && (Flags.AllKnownNonNegative || Flags.HasNUW))
diff --git a/llvm/test/Transforms/Reassociate/reassoc-mul-nuw.ll b/llvm/test/Transforms/Reassociate/reassoc-mul-nuw.ll
index 79cd57c292ce6..3ee6ffe2f22b8 100644
--- a/llvm/test/Transforms/Reassociate/reassoc-mul-nuw.ll
+++ b/llvm/test/Transforms/Reassociate/reassoc-mul-nuw.ll
@@ -21,8 +21,8 @@ define i4 @nuw_preserve_non_zero(i4 %a, i4 %b, i4 %c) {
; CHECK-NEXT: [[A0:%.*]] = add nuw i4 [[A]], 1
; CHECK-NEXT: [[B0:%.*]] = add nuw i4 [[B]], 1
; CHECK-NEXT: [[C0:%.*]] = add nuw i4 [[C]], 1
-; CHECK-NEXT: [[V0:%.*]] = mul i4 [[B0]], [[A0]]
-; CHECK-NEXT: [[V1:%.*]] = mul i4 [[V0]], [[C0]]
+; CHECK-NEXT: [[V0:%.*]] = mul nuw i4 [[B0]], [[A0]]
+; CHECK-NEXT: [[V1:%.*]] = mul nuw i4 [[V0]], [[C0]]
; CHECK-NEXT: ret i4 [[V1]]
;
%a0 = add nuw i4 %a, 1
@@ -40,9 +40,9 @@ define i4 @re_order_mul_nuw(i4 %xx0, i4 %xx1, i4 %xx2, i4 %xx3) {
; CHECK-NEXT: [[X1:%.*]] = add nuw i4 [[XX1]], 1
; CHECK-NEXT: [[X2:%.*]] = add nuw i4 [[XX2]], 1
; CHECK-NEXT: [[X3:%.*]] = add nuw i4 [[XX3]], 1
-; CHECK-NEXT: [[MUL_B:%.*]] = mul i4 [[X1]], [[X0]]
-; CHECK-NEXT: [[MUL_A:%.*]] = mul i4 [[MUL_B]], [[X2]]
-; CHECK-NEXT: [[MUL_C:%.*]] = mul i4 [[MUL_A]], [[X3]]
+; CHECK-NEXT: [[MUL_B:%.*]] = mul nuw i4 [[X1]], [[X0]]
+; CHECK-NEXT: [[MUL_A:%.*]] = mul nuw i4 [[MUL_B]], [[X2]]
+; CHECK-NEXT: [[MUL_C:%.*]] = mul nuw i4 [[MUL_A]], [[X3]]
; CHECK-NEXT: ret i4 [[MUL_C]]
;
%x0 = add nuw i4 %xx0, 1
@@ -88,9 +88,9 @@ define i4 @re_order_mul_nsw(i4 %xx0, i4 %xx1, i4 %xx2, i4 %xx3) {
; CHECK-NEXT: [[X1:%.*]] = call i4 @llvm.smax.i4(i4 [[X1_NZ]], i4 1)
; CHECK-NEXT: [[X2:%.*]] = call i4 @llvm.smax.i4(i4 [[X2_NZ]], i4 1)
; CHECK-NEXT: [[X3:%.*]] = call i4 @llvm.smax.i4(i4 [[X3_NZ]], i4 1)
-; CHECK-NEXT: [[MUL_B:%.*]] = mul i4 [[X1]], [[X0]]
-; CHECK-NEXT: [[MUL_A:%.*]] = mul i4 [[MUL_B]], [[X2]]
-; CHECK-NEXT: [[MUL_C:%.*]] = mul i4 [[MUL_A]], [[X3]]
+; CHECK-NEXT: [[MUL_B:%.*]] = mul nsw i4 [[X1]], [[X0]]
+; CHECK-NEXT: [[MUL_A:%.*]] = mul nsw i4 [[MUL_B]], [[X2]]
+; CHECK-NEXT: [[MUL_C:%.*]] = mul nsw i4 [[MUL_A]], [[X3]]
; CHECK-NEXT: ret i4 [[MUL_C]]
;
%x0_nz = add nuw i4 %xx0, 1
@@ -114,9 +114,9 @@ define i4 @re_order_mul_nsw_nuw(i4 %xx0, i4 %xx1, i4 %xx2, i4 %xx3) {
; CHECK-NEXT: [[X1:%.*]] = add nuw i4 [[XX1]], 1
; CHECK-NEXT: [[X2:%.*]] = add nuw i4 [[XX2]], 1
; CHECK-NEXT: [[X3:%.*]] = add nuw i4 [[XX3]], 1
-; CHECK-NEXT: [[MUL_B:%.*]] = mul i4 [[X1]], [[X0]]
-; CHECK-NEXT: [[MUL_A:%.*]] = mul i4 [[MUL_B]], [[X2]]
-; CHECK-NEXT: [[MUL_C:%.*]] = mul i4 [[MUL_A]], [[X3]]
+; CHECK-NEXT: [[MUL_B:%.*]] = mul nuw nsw i4 [[X1]], [[X0]]
+; CHECK-NEXT: [[MUL_A:%.*]] = mul nuw nsw i4 [[MUL_B]], [[X2]]
+; CHECK-NEXT: [[MUL_C:%.*]] = mul nuw nsw i4 [[MUL_A]], [[X3]]
; CHECK-NEXT: ret i4 [[MUL_C]]
;
%x0 = add nuw i4 %xx0, 1
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