[InstCombine] Missed optimization in math expression: squashing sqrt functions
Summary: This patch enables folding under -ffast-math flag sqrt(a) * sqrt(b) -> sqrt(a*b)
Reviewers: hfinkel, spatel, davide
Reviewed By: spatel, davide
Subscribers: davide, llvm-commits
Differential Revision: https://reviews.llvm.org/D41322
llvm-svn: 321637
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 541dde6..3860483 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -728,6 +728,23 @@
}
}
+ // sqrt(a) * sqrt(b) -> sqrt(a * b)
+ if (AllowReassociate &&
+ Op0->hasOneUse() && Op1->hasOneUse()) {
+ Value *Opnd0 = nullptr;
+ Value *Opnd1 = nullptr;
+ if (match(Op0, m_Intrinsic<Intrinsic::sqrt>(m_Value(Opnd0))) &&
+ match(Op1, m_Intrinsic<Intrinsic::sqrt>(m_Value(Opnd1)))) {
+ BuilderTy::FastMathFlagGuard Guard(Builder);
+ Builder.setFastMathFlags(I.getFastMathFlags());
+ Value *FMulVal = Builder.CreateFMul(Opnd0, Opnd1);
+ Value *Sqrt = Intrinsic::getDeclaration(I.getModule(),
+ Intrinsic::sqrt, I.getType());
+ Value *SqrtCall = Builder.CreateCall(Sqrt, FMulVal);
+ return replaceInstUsesWith(I, SqrtCall);
+ }
+ }
+
// Handle symmetric situation in a 2-iteration loop
Value *Opnd0 = Op0;
Value *Opnd1 = Op1;
diff --git a/llvm/test/Transforms/InstCombine/fmul-sqrt.ll b/llvm/test/Transforms/InstCombine/fmul-sqrt.ll
new file mode 100644
index 0000000..0031a61
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/fmul-sqrt.ll
@@ -0,0 +1,67 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+declare double @llvm.sqrt.f64(double) nounwind readnone speculatable
+declare void @use(double)
+
+; sqrt(a) * sqrt(b) no math flags
+define double @sqrt_a_sqrt_b(double %a, double %b) {
+; CHECK-LABEL: @sqrt_a_sqrt_b(
+; CHECK-NEXT: [[TMP1:%.*]] = call double @llvm.sqrt.f64(double [[A:%.*]])
+; CHECK-NEXT: [[TMP2:%.*]] = call double @llvm.sqrt.f64(double [[B:%.*]])
+; CHECK-NEXT: [[MUL:%.*]] = fmul double [[TMP1]], [[TMP2]]
+; CHECK-NEXT: ret double [[MUL]]
+;
+ %1 = call double @llvm.sqrt.f64(double %a)
+ %2 = call double @llvm.sqrt.f64(double %b)
+ %mul = fmul double %1, %2
+ ret double %mul
+}
+
+; sqrt(a) * sqrt(b) fast-math, multiple uses
+define double @sqrt_a_sqrt_b_multiple_uses(double %a, double %b) {
+; CHECK-LABEL: @sqrt_a_sqrt_b_multiple_uses(
+; CHECK-NEXT: [[TMP1:%.*]] = call fast double @llvm.sqrt.f64(double [[A:%.*]])
+; CHECK-NEXT: [[TMP2:%.*]] = call fast double @llvm.sqrt.f64(double [[B:%.*]])
+; CHECK-NEXT: [[MUL:%.*]] = fmul fast double [[TMP1]], [[TMP2]]
+; CHECK-NEXT: call void @use(double [[TMP2]])
+; CHECK-NEXT: ret double [[MUL]]
+;
+ %1 = call fast double @llvm.sqrt.f64(double %a)
+ %2 = call fast double @llvm.sqrt.f64(double %b)
+ %mul = fmul fast double %1, %2
+ call void @use(double %2)
+ ret double %mul
+}
+
+; sqrt(a) * sqrt(b) => sqrt(a*b) with fast-math
+define double @sqrt_a_sqrt_b_fast(double %a, double %b) {
+; CHECK-LABEL: @sqrt_a_sqrt_b_fast(
+; CHECK-NEXT: [[TMP1:%.*]] = fmul fast double [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = call fast double @llvm.sqrt.f64(double [[TMP1]])
+; CHECK-NEXT: ret double [[TMP2]]
+;
+ %1 = call fast double @llvm.sqrt.f64(double %a)
+ %2 = call fast double @llvm.sqrt.f64(double %b)
+ %mul = fmul fast double %1, %2
+ ret double %mul
+}
+
+; sqrt(a) * sqrt(b) * sqrt(c) * sqrt(d) => sqrt(a*b*c+d) with fast-math
+define double @sqrt_a_sqrt_b_sqrt_c_sqrt_d_fast(double %a, double %b, double %c, double %d) {
+; CHECK-LABEL: @sqrt_a_sqrt_b_sqrt_c_sqrt_d_fast(
+; CHECK-NEXT: [[TMP1:%.*]] = fmul fast double [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = fmul fast double [[TMP1]], [[C:%.*]]
+; CHECK-NEXT: [[TMP3:%.*]] = fmul fast double [[TMP2]], [[D:%.*]]
+; CHECK-NEXT: [[TMP4:%.*]] = call fast double @llvm.sqrt.f64(double [[TMP3]])
+; CHECK-NEXT: ret double [[TMP4]]
+;
+ %1 = call fast double @llvm.sqrt.f64(double %a)
+ %2 = call fast double @llvm.sqrt.f64(double %b)
+ %mul = fmul fast double %1, %2
+ %3 = call fast double @llvm.sqrt.f64(double %c)
+ %mul1 = fmul fast double %mul, %3
+ %4 = call fast double @llvm.sqrt.f64(double %d)
+ %mul2 = fmul fast double %mul1, %4
+ ret double %mul2
+}