[PATCH] D12882: [SimplifyCFG] do not speculate fdiv by default; it's expensive (PR24818)

[Sanjay Patel via llvm-commits]

spatel updated this revision to Diff 34810.
spatel added a comment.

Updated patch: full-context diff.


http://reviews.llvm.org/D12882

Files:
  include/llvm/Analysis/TargetTransformInfoImpl.h
  test/Transforms/SimplifyCFG/speculate-math.ll

Index: test/Transforms/SimplifyCFG/speculate-math.ll
===================================================================
--- test/Transforms/SimplifyCFG/speculate-math.ll
+++ test/Transforms/SimplifyCFG/speculate-math.ll
@@ -7,6 +7,24 @@
 declare float @llvm.minnum.f32(float, float) nounwind readonly
 declare float @llvm.maxnum.f32(float, float) nounwind readonly
 
+; Do not speculate fdiv by default because it is generally expensive. 
+
+; CHECK-LABEL: @fdiv_test(
+; CHECK-NOT: select
+define double @fdiv_test(double %a, double %b) {
+entry:
+  %cmp = fcmp ogt double %a, 0.0
+  br i1 %cmp, label %cond.true, label %cond.end
+
+cond.true:
+  %div = fdiv double %b, %a
+  br label %cond.end
+
+cond.end:
+  %cond = phi double [ %div, %cond.true ], [ 0.0, %entry ]
+  ret double %cond
+}
+
 ; CHECK-LABEL: @sqrt_test(
 ; CHECK: select
 define void @sqrt_test(float addrspace(1)* noalias nocapture %out, float %a) nounwind {
Index: include/llvm/Analysis/TargetTransformInfoImpl.h
===================================================================
--- include/llvm/Analysis/TargetTransformInfoImpl.h
+++ include/llvm/Analysis/TargetTransformInfoImpl.h
@@ -61,6 +61,10 @@
       // Otherwise, the default basic cost is used.
       return TTI::TCC_Basic;
 
+    // FIXME: UDiv and SDiv should also default to expensive.
+    case Instruction::FDiv:
+      return TTI::TCC_Expensive;
+
     case Instruction::IntToPtr: {
       // An inttoptr cast is free so long as the input is a legal integer type
       // which doesn't contain values outside the range of a pointer.


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