From ac349fb9d87d1a0344ec2b8897788e794ccdd455 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Sun, 10 Dec 2017 17:25:54 +0000
Subject: [PATCH] [SimplifyLibCalls] propagate FMF when folding pow(x, -1.0)
 call

Follow-up for a bug that's similar to:
https://bugs.llvm.org/show_bug.cgi?id=35601


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320312 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyLibCalls.cpp | 25 ++++++++++-------------
 test/Transforms/InstCombine/pow-1.ll      |  2 +-
 2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 273a5e79a7d..60f6c600b5a 100644
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1204,16 +1204,17 @@ Value *LibCallSimplifier::optimizePow(CallInst *CI, IRBuilder<> &B) {
     return Sel;
   }
 
-  if (Op2C->isExactlyValue(1.0)) // pow(x, 1.0) -> x
+  // Propagate fast-math-flags from the call to any created instructions.
+  IRBuilder<>::FastMathFlagGuard Guard(B);
+  B.setFastMathFlags(CI->getFastMathFlags());
+  // pow(x, 1.0) --> x
+  if (Op2C->isExactlyValue(1.0))
     return Op1;
-  if (Op2C->isExactlyValue(2.0)) {
-    // pow(x, 2.0) --> x * x
-    IRBuilder<>::FastMathFlagGuard Guard(B);
-    B.setFastMathFlags(CI->getFastMathFlags());
+  // pow(x, 2.0) --> x * x
+  if (Op2C->isExactlyValue(2.0))
     return B.CreateFMul(Op1, Op1, "pow2");
-  }
-  // FIXME: This should propagate the FMF of the call to the fdiv.
-  if (Op2C->isExactlyValue(-1.0)) // pow(x, -1.0) -> 1.0/x
+  // pow(x, -1.0) --> 1.0 / x
+  if (Op2C->isExactlyValue(-1.0))
     return B.CreateFDiv(ConstantFP::get(CI->getType(), 1.0), Op1, "powrecip");
 
   // In -ffast-math, generate repeated fmul instead of generating pow(x, n).
@@ -1225,10 +1226,6 @@ Value *LibCallSimplifier::optimizePow(CallInst *CI, IRBuilder<> &B) {
         !V.isInteger())
       return nullptr;
 
-    // Propagate fast math flags.
-    IRBuilder<>::FastMathFlagGuard Guard(B);
-    B.setFastMathFlags(CI->getFastMathFlags());
-
     // We will memoize intermediate products of the Addition Chain.
     Value *InnerChain[33] = {nullptr};
     InnerChain[1] = Op1;
@@ -1236,8 +1233,8 @@ Value *LibCallSimplifier::optimizePow(CallInst *CI, IRBuilder<> &B) {
 
     // We cannot readily convert a non-double type (like float) to a double.
     // So we first convert V to something which could be converted to double.
-    bool ignored;
-    V.convert(APFloat::IEEEdouble(), APFloat::rmTowardZero, &ignored);
+    bool Ignored;
+    V.convert(APFloat::IEEEdouble(), APFloat::rmTowardZero, &Ignored);
     
     Value *FMul = getPow(InnerChain, V.convertToDouble(), B);
     // For negative exponents simply compute the reciprocal.
diff --git a/test/Transforms/InstCombine/pow-1.ll b/test/Transforms/InstCombine/pow-1.ll
index 3559828058b..eef4f76fb84 100644
--- a/test/Transforms/InstCombine/pow-1.ll
+++ b/test/Transforms/InstCombine/pow-1.ll
@@ -166,7 +166,7 @@ define float @pow_neg1_strict(float %x) {
 
 define double @pow_neg1_double_fast(double %x) {
 ; CHECK-LABEL: @pow_neg1_double_fast(
-; CHECK-NEXT:    [[POWRECIP:%.*]] = fdiv double 1.000000e+00, %x
+; CHECK-NEXT:    [[POWRECIP:%.*]] = fdiv fast double 1.000000e+00, %x
 ; CHECK-NEXT:    ret double [[POWRECIP]]
 ;
   %r = call fast double @pow(double %x, double -1.0)
-- 
2.50.1