[InstCombine] Missed optimization in math expression: simplify calls exp functions

Summary: This patch enables folding following expressions under -ffast-math flag: exp(X) * exp(Y) -> exp(X + Y), exp2(X) * exp2(Y) -> exp2(X + Y). Motivation: https://bugs.llvm.org/show_bug.cgi?id=35594

Reviewers: hfinkel, spatel, efriedma, lebedev.ri

Reviewed By: spatel, lebedev.ri

Subscribers: lebedev.ri, llvm-commits

Differential Revision: https://reviews.llvm.org/D41342

llvm-svn: 352730

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index ca67348d05c..ae3f081f508 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -441,6 +441,26 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
       return replaceInstUsesWith(I, Sqrt);
     }
 
+    // exp(X) * exp(Y) -> exp(X + Y)
+    // Match as long as at least one of exp has only one use.
+    if (match(Op0, m_Intrinsic<Intrinsic::exp>(m_Value(X))) &&
+        match(Op1, m_Intrinsic<Intrinsic::exp>(m_Value(Y))) &&
+        (Op0->hasOneUse() || Op1->hasOneUse())) {
+      Value *XY = Builder.CreateFAddFMF(X, Y, &I);
+      Value *Exp = Builder.CreateUnaryIntrinsic(Intrinsic::exp, XY, &I);
+      return replaceInstUsesWith(I, Exp);
+    }
+
+    // exp2(X) * exp2(Y) -> exp2(X + Y)
+    // Match as long as at least one of exp2 has only one use.
+    if (match(Op0, m_Intrinsic<Intrinsic::exp2>(m_Value(X))) &&
+        match(Op1, m_Intrinsic<Intrinsic::exp2>(m_Value(Y))) &&
+        (Op0->hasOneUse() || Op1->hasOneUse())) {
+      Value *XY = Builder.CreateFAddFMF(X, Y, &I);
+      Value *Exp2 = Builder.CreateUnaryIntrinsic(Intrinsic::exp2, XY, &I);
+      return replaceInstUsesWith(I, Exp2);
+    }
+
     // (X*Y) * X => (X*X) * Y where Y != X
     //  The purpose is two-fold:
     //   1) to form a power expression (of X).