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Improve on r192635, ExeDepsFix for avx, and add a test case.

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rdar:15221834 False AVX register dependencies cause 5x slowdown on
flops-5/6 and significant slowdown on several others.

This was blocking the switch to MI-Sched.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192669 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2013-10-15 03:39:43 +00:00
parent cc3d76d982
commit 51dee24ca6
2 changed files with 32 additions and 1 deletions
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4
lib/CodeGen/ExecutionDepsFix.cpp
View File

@ -557,6 +557,9 @@ void ExeDepsFix::processUndefReads(MachineBasicBlock *MBB) {
for (MachineBasicBlock::reverse_iterator I = MBB->rbegin(), E = MBB->rend();
I != E; ++I) {
// Update liveness, including the current instrucion's defs.
LiveUnits.stepBackward(*I, *TRI);
if (UndefMI == &*I) {
if (!LiveUnits.contains(UndefMI->getOperand(OpIdx).getReg(), *TRI))
TII->breakPartialRegDependency(UndefMI, OpIdx, TRI);
@ -568,7 +571,6 @@ void ExeDepsFix::processUndefReads(MachineBasicBlock *MBB) {
UndefMI = UndefReads.back().first;
OpIdx = UndefReads.back().second;
}
LiveUnits.stepBackward(*I, *TRI);
}
}

29
test/CodeGen/X86/break-avx-dep.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: llc < %s -march=x86-64 -mattr=+avx | FileCheck %s
;
; rdar:15221834 False AVX register dependencies cause 5x slowdown on
; flops-6. Make sure the unused register read by vcvtsi2sdq is zeroed
; to avoid cyclic dependence on a write to the same register in a
; previous iteration.
; CHECK-LABEL: t1:
; CHECK-LABEL: %loop
; CHECK: vxorps %[[REG:xmm.]], %{{xmm.}}, %{{xmm.}}
; CHECK: vcvtsi2sdq %{{r..}}, %[[REG]], %{{xmm.}}
define i64 @t1(i64* nocapture %x, double* nocapture %y) nounwind {
entry:
%vx = load i64* %x
br label %loop
loop:
%i = phi i64 [ 1, %entry ], [ %inc, %loop ]
%s1 = phi i64 [ %vx, %entry ], [ %s2, %loop ]
%fi = sitofp i64 %i to double
%vy = load double* %y
%fipy = fadd double %fi, %vy
%iipy = fptosi double %fipy to i64
%s2 = add i64 %s1, %iipy
%inc = add nsw i64 %i, 1
%exitcond = icmp eq i64 %inc, 156250000
br i1 %exitcond, label %ret, label %loop
ret:
ret i64 %s2
}