[PATCH] D62747: [InlineCost] Don't add the soft float functional call cost for the fneg idiom, fsub -0.0, %x

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: efriedma, cameron.mcinally.
Herald added subscribers: haicheng, hiraditya, eraman, javed.absar.
Herald added a project: LLVM.

Fneg can be implemented with an xor rather than a function call so we don't need to add the function call overhead. This was pointed out in D62699 <https://reviews.llvm.org/D62699>


https://reviews.llvm.org/D62747

Files:
  llvm/lib/Analysis/InlineCost.cpp
  llvm/test/Transforms/Inline/ARM/inline-fp.ll


Index: llvm/test/Transforms/Inline/ARM/inline-fp.ll
===================================================================
--- llvm/test/Transforms/Inline/ARM/inline-fp.ll
+++ llvm/test/Transforms/Inline/ARM/inline-fp.ll
@@ -12,6 +12,8 @@
 ; NOFP-DAG: double not inlined into test_double because too costly to inline (cost=125, threshold=75)
 ; NOFP-DAG: single_force_soft not inlined into test_single_force_soft because too costly to inline (cost=125, threshold=75)
 ; NOFP-DAG: single_force_soft not inlined into test_single_force_soft because too costly to inline (cost=125, threshold=75)
+; NOFP-DAG: single_force_soft_fneg not inlined into test_single_force_soft_fneg because too costly to inline (cost=100, threshold=75)
+; NOFP-DAG: single_force_soft_fneg not inlined into test_single_force_soft_fneg because too costly to inline (cost=100, threshold=75)
 
 ; FULLFP-DAG: single inlined into test_single with (cost=0, threshold=75)
 ; FULLFP-DAG: single inlined into test_single with (cost=-15000, threshold=75)
@@ -21,6 +23,8 @@
 ; FULLFP-DAG: double inlined into test_double with (cost=-15000, threshold=75)
 ; FULLFP-DAG: single_force_soft not inlined into test_single_force_soft because too costly to inline (cost=125, threshold=75)
 ; FULLFP-DAG: single_force_soft not inlined into test_single_force_soft because too costly to inline (cost=125, threshold=75)
+; FULLFP-DAG: single_force_soft_fneg not inlined into test_single_force_soft_fneg because too costly to inline (cost=100, threshold=75)
+; FULLFP-DAG: single_force_soft_fneg not inlined into test_single_force_soft_fneg because too costly to inline (cost=100, threshold=75)
 
 ; SINGLEFP-DAG: single inlined into test_single with (cost=0, threshold=75)
 ; SINGLEFP-DAG: single inlined into test_single with (cost=-15000, threshold=75)
@@ -30,6 +34,8 @@
 ; SINGLEFP-DAG: double not inlined into test_double because too costly to inline (cost=125, threshold=75)
 ; SINGLEFP-DAG: single_force_soft not inlined into test_single_force_soft because too costly to inline (cost=125, threshold=75)
 ; SINGLEFP-DAG: single_force_soft not inlined into test_single_force_soft because too costly to inline (cost=125, threshold=75)
+; SINGLEFP-DAG: single_force_soft_fneg not inlined into test_single_force_soft_fneg because too costly to inline (cost=100, threshold=75)
+; SINGLEFP-DAG: single_force_soft_fneg not inlined into test_single_force_soft_fneg because too costly to inline (cost=100, threshold=75)
 
 define i32 @test_single(i32 %a, i8 %b, i32 %c, i8 %d) #0 {
   %call = call float @single(i32 %a, i8 zeroext %b)
@@ -55,6 +61,12 @@
   ret i32 0
 }
 
+define i32 @test_single_force_soft_fneg(i32 %a, i8 %b, i32 %c, i8 %d) #1 {
+  %call = call float @single_force_soft_fneg(i32 %a, i8 zeroext %b) #1
+  %call2 = call float @single_force_soft_fneg(i32 %c, i8 zeroext %d) #1
+  ret i32 0
+}
+
 define internal float @single(i32 %response, i8 zeroext %value1) #0 {
 entry:
   %conv = zext i8 %value1 to i32
@@ -106,6 +118,19 @@
   ret float %div
 }
 
+define internal float @single_force_soft_fneg(i32 %response, i8 zeroext %value1) #1 {
+entry:
+  %conv = zext i8 %value1 to i32
+  %sub = add nsw i32 %conv, -1
+  %conv1 = sitofp i32 %sub to float
+  %0 = tail call float @llvm.pow.f32(float 0x3FF028F5C0000000, float %conv1)
+  %mul = fsub float -0.0, %0
+  %conv2 = sitofp i32 %response to float
+  %sub3 = fsub float %conv2, %mul
+  %div = fdiv float %sub3, %mul
+  ret float %div
+}
+
 declare float @llvm.pow.f32(float, float) optsize minsize
 declare double @llvm.pow.f64(double, double) optsize minsize
 
Index: llvm/lib/Analysis/InlineCost.cpp
===================================================================
--- llvm/lib/Analysis/InlineCost.cpp
+++ llvm/lib/Analysis/InlineCost.cpp
@@ -35,6 +35,7 @@
 #include "llvm/IR/InstVisitor.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Operator.h"
+#include "llvm/IR/PatternMatch.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -1095,9 +1096,11 @@
 
   // If the instruction is floating point, and the target says this operation
   // is expensive, this may eventually become a library call. Treat the cost
-  // as such.
+  // as such. Unless its fneg which can be implemented with an xor.
+  using namespace llvm::PatternMatch;
   if (I.getType()->isFloatingPointTy() &&
-      TTI.getFPOpCost(I.getType()) == TargetTransformInfo::TCC_Expensive)
+      TTI.getFPOpCost(I.getType()) == TargetTransformInfo::TCC_Expensive &&
+      !match(&I, m_FNeg(m_Value())))
     addCost(InlineConstants::CallPenalty);
 
   return false;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D62747.202474.patch
Type: text/x-patch
Size: 4585 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190531/6cf5379a/attachment.bin>