1Pull in r248439 from upstream llvm trunk (by Sanjay Patel): 2 3 set div/rem default values to 'expensive' in TargetTransformInfo's 4 cost model 5 6 ...because that's what the cost model was intended to do. 7 8 As discussed in D12882, this fix has a temporary unintended 9 consequence for SimplifyCFG: it causes us to not speculate an fdiv. 10 However, two wrongs make PR24818 right, and two wrongs make PR24343 11 act right even though it's really still wrong. 12 13 I intend to correct SimplifyCFG and add to CodeGenPrepare to account 14 for this cost model change and preserve the righteousness for the bug 15 report cases. 16 17 https://llvm.org/bugs/show_bug.cgi?id=24818 18 https://llvm.org/bugs/show_bug.cgi?id=24343 19 20 Differential Revision: http://reviews.llvm.org/D12882 21 22This fixes the too-eager fdiv hoisting in pow(), which could lead to 23unexpected floating point exceptions. 24 25Introduced here: http://svnweb.freebsd.org/changeset/base/288195 26 27Index: include/llvm/Analysis/TargetTransformInfoImpl.h 28=================================================================== 29--- include/llvm/Analysis/TargetTransformInfoImpl.h 30+++ include/llvm/Analysis/TargetTransformInfoImpl.h 31@@ -60,6 +60,14 @@ class TargetTransformInfoImplBase { 32 // Otherwise, the default basic cost is used. 33 return TTI::TCC_Basic; 34 35+ case Instruction::FDiv: 36+ case Instruction::FRem: 37+ case Instruction::SDiv: 38+ case Instruction::SRem: 39+ case Instruction::UDiv: 40+ case Instruction::URem: 41+ return TTI::TCC_Expensive; 42+ 43 case Instruction::IntToPtr: { 44 // An inttoptr cast is free so long as the input is a legal integer type 45 // which doesn't contain values outside the range of a pointer. 46Index: test/Transforms/SimplifyCFG/speculate-math.ll 47=================================================================== 48--- test/Transforms/SimplifyCFG/speculate-math.ll 49+++ test/Transforms/SimplifyCFG/speculate-math.ll 50@@ -7,6 +7,33 @@ declare float @llvm.fabs.f32(float) nounwind reado 51 declare float @llvm.minnum.f32(float, float) nounwind readonly 52 declare float @llvm.maxnum.f32(float, float) nounwind readonly 53 54+; FIXME: This is intended to be a temporary test. As discussed in 55+; D12882, we actually do want to speculate even expensive operations 56+; in SimplifyCFG because it can expose more optimizations for other 57+; passes. Therefore, we either need to adjust SimplifyCFG's 58+; calculations that use the TTI cost model or use a different cost 59+; model for deciding which ops should be speculated in SimplifyCFG. 60+; We should also be using the TTI cost model later - for example in 61+; CodeGenPrepare - to potentially undo this speculation. 62+ 63+; Do not speculate fdiv by default because it is generally expensive. 64+ 65+; CHECK-LABEL: @fdiv_test( 66+; CHECK-NOT: select 67+define double @fdiv_test(double %a, double %b) { 68+entry: 69+ %cmp = fcmp ogt double %a, 0.0 70+ br i1 %cmp, label %cond.true, label %cond.end 71+ 72+cond.true: 73+ %div = fdiv double %b, %a 74+ br label %cond.end 75+ 76+cond.end: 77+ %cond = phi double [ %div, %cond.true ], [ 0.0, %entry ] 78+ ret double %cond 79+} 80+ 81 ; CHECK-LABEL: @sqrt_test( 82 ; CHECK: select 83 define void @sqrt_test(float addrspace(1)* noalias nocapture %out, float %a) nounwind { 84