[llvm] Fold tan(x) * cos(x) -> sin(x) (PR #136319)
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Fri Apr 18 09:15:26 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: None (amordo)
<details>
<summary>Changes</summary>
This patch enables folding tan(x) * cos(x) -> sin(x) under -ffast-math flag.
Alive2 proof is not able to check the transformation - https://alive2.llvm.org/ce/z/sgMYRJ
Seems (some) intrinsics are not supported by it, should mention in [the doc](https://llvm.org/docs/InstCombineContributorGuide.html#proofs)?
The tests copy logic from https://github.com/llvm/llvm-project/blob/6c5f50f18694a4d91d7ce53a14188c54ee7c6f3b/llvm/test/Transforms/InstCombine/fdiv-sin-cos.ll
Fixes https://github.com/llvm/llvm-project/issues/34950.
---
Full diff: https://github.com/llvm/llvm-project/pull/136319.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (+10)
- (added) llvm/test/Transforms/InstCombine/fmul-tan-cos.ll (+123)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index c7023eb79b04e..e3ba0c4468d92 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1073,6 +1073,16 @@ Instruction *InstCombinerImpl::visitFMul(BinaryOperator &I) {
return Result;
}
+ // tan(X) * cos(X) -> sin(X)
+ if (I.hasAllowReassoc() && Op0->hasOneUse() && Op1->hasOneUse()) {
+ Value *X;
+ if (match(Op0, m_Intrinsic<Intrinsic::tan>(m_Value(X))) &&
+ match(Op1, m_Intrinsic<Intrinsic::cos>(m_Specific(X)))) {
+ Value *Sin = Builder.CreateUnaryIntrinsic(Intrinsic::sin, X, &I);
+ return replaceInstUsesWith(I, Sin);
+ }
+ }
+
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/fmul-tan-cos.ll b/llvm/test/Transforms/InstCombine/fmul-tan-cos.ll
new file mode 100644
index 0000000000000..8196e8f7c81ba
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/fmul-tan-cos.ll
@@ -0,0 +1,123 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+define double @fmul_tan_cos(double %a) {
+; CHECK-LABEL: define double @fmul_tan_cos(
+; CHECK-SAME: double [[A:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = call double @llvm.tan.f64(double [[A]])
+; CHECK-NEXT: [[TMP2:%.*]] = call double @llvm.cos.f64(double [[A]])
+; CHECK-NEXT: [[RES:%.*]] = fmul double [[TMP1]], [[TMP2]]
+; CHECK-NEXT: ret double [[RES]]
+;
+ %1 = call double @llvm.tan.f64(double %a)
+ %2 = call double @llvm.cos.f64(double %a)
+ %res = fmul double %1, %2
+ ret double %res
+}
+
+define double @fmul_strict_tan_strict_cos_reassoc(double %a) {
+; CHECK-LABEL: define double @fmul_strict_tan_strict_cos_reassoc(
+; CHECK-SAME: double [[A:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = call double @llvm.tan.f64(double [[A]])
+; CHECK-NEXT: [[TMP2:%.*]] = call reassoc double @llvm.cos.f64(double [[A]])
+; CHECK-NEXT: [[RES:%.*]] = fmul double [[TMP1]], [[TMP2]]
+; CHECK-NEXT: ret double [[RES]]
+;
+ %1 = call double @llvm.tan.f64(double %a)
+ %2 = call reassoc double @llvm.cos.f64(double %a)
+ %res = fmul double %1, %2
+ ret double %res
+}
+
+define double @fmul_reassoc_tan_strict_cos_strict(double %a, ptr dereferenceable(2) %dummy) {
+; CHECK-LABEL: define double @fmul_reassoc_tan_strict_cos_strict(
+; CHECK-SAME: double [[A:%.*]], ptr dereferenceable(2) [[DUMMY:%.*]]) {
+; CHECK-NEXT: [[RES:%.*]] = call reassoc double @llvm.sin.f64(double [[A]])
+; CHECK-NEXT: ret double [[RES]]
+;
+ %1 = call double @llvm.tan.f64(double %a)
+ %2 = call double @llvm.cos.f64(double %a)
+ %res = fmul reassoc double %1, %2
+ ret double %res
+}
+
+define double @fmul_reassoc_tan_reassoc_cos_strict(double %a) {
+; CHECK-LABEL: define double @fmul_reassoc_tan_reassoc_cos_strict(
+; CHECK-SAME: double [[A:%.*]]) {
+; CHECK-NEXT: [[RES:%.*]] = call reassoc double @llvm.sin.f64(double [[A]])
+; CHECK-NEXT: ret double [[RES]]
+;
+ %1 = call reassoc double @llvm.tan.f64(double %a)
+ %2 = call double @llvm.cos.f64(double %a)
+ %res = fmul reassoc double %1, %2
+ ret double %res
+}
+
+define double @fmul_tan_cos_reassoc_multiple_uses(double %a) {
+; CHECK-LABEL: define double @fmul_tan_cos_reassoc_multiple_uses(
+; CHECK-SAME: double [[A:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = call reassoc double @llvm.tan.f64(double [[A]])
+; CHECK-NEXT: [[TMP2:%.*]] = call reassoc double @llvm.cos.f64(double [[A]])
+; CHECK-NEXT: [[RES:%.*]] = fmul reassoc double [[TMP1]], [[TMP2]]
+; CHECK-NEXT: call void @use(double [[TMP2]])
+; CHECK-NEXT: ret double [[RES]]
+;
+ %1 = call reassoc double @llvm.tan.f64(double %a)
+ %2 = call reassoc double @llvm.cos.f64(double %a)
+ %res = fmul reassoc double %1, %2
+ call void @use(double %2)
+ ret double %res
+}
+
+define double @fmul_tan_cos_reassoc(double %a) {
+; CHECK-LABEL: define double @fmul_tan_cos_reassoc(
+; CHECK-SAME: double [[A:%.*]]) {
+; CHECK-NEXT: [[RES:%.*]] = call reassoc double @llvm.sin.f64(double [[A]])
+; CHECK-NEXT: ret double [[RES]]
+;
+ %1 = call reassoc double @llvm.tan.f64(double %a)
+ %2 = call reassoc double @llvm.cos.f64(double %a)
+ %res = fmul reassoc double %1, %2
+ ret double %res
+}
+
+define float @fmul_tanf_cosf_reassoc(float %a) {
+; CHECK-LABEL: define float @fmul_tanf_cosf_reassoc(
+; CHECK-SAME: float [[A:%.*]]) {
+; CHECK-NEXT: [[RES:%.*]] = call reassoc float @llvm.sin.f32(float [[A]])
+; CHECK-NEXT: ret float [[RES]]
+;
+ %1 = call reassoc float @llvm.tan.f32(float %a)
+ %2 = call reassoc float @llvm.cos.f32(float %a)
+ %res = fmul reassoc float %1, %2
+ ret float %res
+}
+
+define fp128 @fmul_tanfp128_cosfp128_reassoc(fp128 %a) {
+; CHECK-LABEL: define fp128 @fmul_tanfp128_cosfp128_reassoc(
+; CHECK-SAME: fp128 [[A:%.*]]) {
+; CHECK-NEXT: [[RES:%.*]] = call reassoc fp128 @llvm.sin.f128(fp128 [[A]])
+; CHECK-NEXT: ret fp128 [[RES]]
+;
+ %1 = call reassoc fp128 @llvm.tan.fp128(fp128 %a)
+ %2 = call reassoc fp128 @llvm.cos.fp128(fp128 %a)
+ %res = fmul reassoc fp128 %1, %2
+ ret fp128 %res
+}
+
+declare double @llvm.sin.f64(double) #1
+declare float @llvm.sin.f32(float) #1
+declare fp128 @llvm.sin.fp128(fp128) #1
+
+declare double @llvm.cos.f64(double) #1
+declare float @llvm.cos.f32(float) #1
+declare fp128 @llvm.cos.fp128(fp128) #1
+
+declare double @llvm.tan.f64(double) #1
+declare float @llvm.tan.f32(float) #1
+declare fp128 @llvm.tan.fp128(fp128) #1
+
+declare void @use(double)
+
+attributes #0 = { nounwind readnone speculatable }
+attributes #1 = { nounwind readnone }
``````````
</details>
https://github.com/llvm/llvm-project/pull/136319
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