From dbd50cefa173b5d2bcfbdb0dd62f3d145d589b44 Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Wed, 23 Sep 2015 22:28:18 +0000 Subject: [PATCH] set div/rem default values to 'expensive' in TargetTransformInfo's cost model ...because that's what the cost model was intended to do. As discussed in D12882, this fix has a temporary unintended consequence for SimplifyCFG: it causes us to not speculate an fdiv. However, two wrongs make PR24818 right, and two wrongs make PR24343 act right even though it's really still wrong. I intend to correct SimplifyCFG and add to CodeGenPrepare to account for this cost model change and preserve the righteousness for the bug report cases. https://llvm.org/bugs/show_bug.cgi?id=24818 https://llvm.org/bugs/show_bug.cgi?id=24343 Differential Revision: http://reviews.llvm.org/D12882 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248439 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../llvm/Analysis/TargetTransformInfoImpl.h | 8 ++++++ test/Transforms/SimplifyCFG/speculate-math.ll | 27 +++++++++++++++++++ 2 files changed, 35 insertions(+) diff --git a/include/llvm/Analysis/TargetTransformInfoImpl.h b/include/llvm/Analysis/TargetTransformInfoImpl.h index e903679259f..506c7f24c1d 100644 --- a/include/llvm/Analysis/TargetTransformInfoImpl.h +++ b/include/llvm/Analysis/TargetTransformInfoImpl.h @@ -61,6 +61,14 @@ public: // Otherwise, the default basic cost is used. return TTI::TCC_Basic; + case Instruction::FDiv: + case Instruction::FRem: + case Instruction::SDiv: + case Instruction::SRem: + case Instruction::UDiv: + case Instruction::URem: + 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. diff --git a/test/Transforms/SimplifyCFG/speculate-math.ll b/test/Transforms/SimplifyCFG/speculate-math.ll index 0ba93d29117..442e8677e97 100644 --- a/test/Transforms/SimplifyCFG/speculate-math.ll +++ b/test/Transforms/SimplifyCFG/speculate-math.ll @@ -7,6 +7,33 @@ declare float @llvm.fabs.f32(float) nounwind readonly declare float @llvm.minnum.f32(float, float) nounwind readonly declare float @llvm.maxnum.f32(float, float) nounwind readonly +; FIXME: This is intended to be a temporary test. As discussed in +; D12882, we actually do want to speculate even expensive operations +; in SimplifyCFG because it can expose more optimizations for other +; passes. Therefore, we either need to adjust SimplifyCFG's +; calculations that use the TTI cost model or use a different cost +; model for deciding which ops should be speculated in SimplifyCFG. +; We should also be using the TTI cost model later - for example in +; CodeGenPrepare - to potentially undo this speculation. + +; 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 { -- 2.34.1