[llvm] [InstCombine] optimize powi(X,Y) * X with Ofast (PR #69998)
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Mon Oct 23 19:35:14 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Allen (vfdff)
<details>
<summary>Changes</summary>
Try to transform the powi(X, Y) * X into powi(X, Y+1) with Ofast
For this case, when the Y is 3, then powi(X, 4) is replaced by X2 = X * X; X2 * X2 in the further step.
Similar to D109954, who requires reassoc.
Fixes https://github.com/llvm/llvm-project/issues/69862.
---
Full diff: https://github.com/llvm/llvm-project/pull/69998.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (+12)
- (modified) llvm/test/Transforms/InstCombine/powi.ll (+49)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index bc784390c23be49..d3b07113ed7a183 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -716,6 +716,18 @@ Instruction *InstCombinerImpl::visitFMul(BinaryOperator &I) {
return replaceInstUsesWith(I, Pow);
}
+ // powi(X, Y) * X --> powi(X, Y+1)
+ // X * powi(X, Y) --> powi(X, Y+1)
+ if (match(&I, m_c_FMul(m_OneUse(m_Intrinsic<Intrinsic::powi>(m_Value(X),
+ m_Value(Y))),
+ m_Deferred(X))) &&
+ willNotOverflowSignedAdd(Y, ConstantInt::get(Y->getType(), 1), I)) {
+ auto *Y1 = Builder.CreateAdd(Y, ConstantInt::get(Y->getType(), 1));
+ auto *NewPow = Builder.CreateIntrinsic(
+ Intrinsic::powi, {X->getType(), Y1->getType()}, {X, Y1}, &I);
+ return replaceInstUsesWith(I, NewPow);
+ }
+
if (I.isOnlyUserOfAnyOperand()) {
// pow(X, Y) * pow(X, Z) -> pow(X, Y + Z)
if (match(Op0, m_Intrinsic<Intrinsic::pow>(m_Value(X), m_Value(Y))) &&
diff --git a/llvm/test/Transforms/InstCombine/powi.ll b/llvm/test/Transforms/InstCombine/powi.ll
index 89efbb6f4536113..95722d09a17ad32 100644
--- a/llvm/test/Transforms/InstCombine/powi.ll
+++ b/llvm/test/Transforms/InstCombine/powi.ll
@@ -341,3 +341,52 @@ define double @fdiv_pow_powi_negative_variable(double %x, i32 %y) {
%div = fdiv reassoc nnan double %p1, %x
ret double %div
}
+
+; powi(X, Y) * X --> powi(X, Y+1)
+define double @powi_fmul_powi_x(double noundef %x) {
+; CHECK-LABEL: @powi_fmul_powi_x(
+; CHECK-NEXT: [[MUL:%.*]] = call reassoc double @llvm.powi.f64.i32(double [[X:%.*]], i32 4)
+; CHECK-NEXT: ret double [[MUL]]
+;
+ %p1 = tail call double @llvm.powi.f64.i32(double %x, i32 3)
+ %mul = fmul reassoc double %p1, %x
+ ret double %mul
+}
+
+; Negative test: Multi-use
+define double @powi_fmul_powi_x_multi_use(double noundef %x) {
+; CHECK-LABEL: @powi_fmul_powi_x_multi_use(
+; CHECK-NEXT: [[P1:%.*]] = tail call double @llvm.powi.f64.i32(double [[X:%.*]], i32 3)
+; CHECK-NEXT: tail call void @use(double [[P1]])
+; CHECK-NEXT: [[MUL:%.*]] = fmul reassoc double [[P1]], [[X]]
+; CHECK-NEXT: ret double [[MUL]]
+;
+ %p1 = tail call double @llvm.powi.f64.i32(double %x, i32 3)
+ tail call void @use(double %p1)
+ %mul = fmul reassoc double %p1, %x
+ ret double %mul
+}
+
+; Negative test: Miss fmf flag
+define double @powi_fmul_powi_x_missing_reassoc(double noundef %x) {
+; CHECK-LABEL: @powi_fmul_powi_x_missing_reassoc(
+; CHECK-NEXT: [[P1:%.*]] = tail call double @llvm.powi.f64.i32(double [[X:%.*]], i32 3)
+; CHECK-NEXT: [[MUL:%.*]] = fmul double [[P1]], [[X]]
+; CHECK-NEXT: ret double [[MUL]]
+;
+ %p1 = tail call double @llvm.powi.f64.i32(double %x, i32 3)
+ %mul = fmul double %p1, %x
+ ret double %mul
+}
+
+; Negative test: overflow
+define double @powi_fmul_powi_x_overflow(double noundef %x) {
+; CHECK-LABEL: @powi_fmul_powi_x_overflow(
+; CHECK-NEXT: [[P1:%.*]] = tail call double @llvm.powi.f64.i32(double [[X:%.*]], i32 2147483647)
+; CHECK-NEXT: [[MUL:%.*]] = fmul reassoc double [[P1]], [[X]]
+; CHECK-NEXT: ret double [[MUL]]
+;
+ %p1 = tail call double @llvm.powi.f64.i32(double %x, i32 2147483647) ; INT_MAX
+ %mul = fmul reassoc double %p1, %x
+ ret double %mul
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/69998
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