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[IRCE] Add an option to skip profitability checks 

If `-irce-skip-profitability-checks` is passed in, IRCE will kick in in
all cases where it is legal for it to kick in.  This flag is intended to
help diagnose and analyse performance issues.

llvm-svn: 276372
This commit is contained in:
Sanjoy Das 2016-07-22 00:40:56 +00:00
parent 0c5b92cae6
commit bb969791b4
2 changed files with 38 additions and 2 deletions
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9
llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
View File

@ -82,6 +82,9 @@ static cl::opt<bool> PrintRangeChecks("irce-print-range-checks", cl::Hidden,
static cl::opt<int> MaxExitProbReciprocal("irce-max-exit-prob-reciprocal",
cl::Hidden, cl::init(10));
static cl::opt<bool> SkipProfitabilityChecks("irce-skip-profitability-checks",
cl::Hidden, cl::init(false));
#define DEBUG_TYPE "irce"
namespace {
@ -392,7 +395,8 @@ void InductiveRangeCheck::extractRangeChecksFromBranch(
BranchProbability LikelyTaken(15, 16);
if (BPI.getEdgeProbability(BI->getParent(), (unsigned)0) < LikelyTaken)
if (!SkipProfitabilityChecks &&
BPI.getEdgeProbability(BI->getParent(), (unsigned)0) < LikelyTaken)
return;
SmallPtrSet<Value *, 8> Visited;
@ -648,7 +652,8 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE, BranchProbabilityInfo &BP
BranchProbability ExitProbability =
BPI.getEdgeProbability(LatchBr->getParent(), LatchBrExitIdx);
if (ExitProbability > BranchProbability(1, MaxExitProbReciprocal)) {
if (!SkipProfitabilityChecks &&
ExitProbability > BranchProbability(1, MaxExitProbReciprocal)) {
FailureReason = "short running loop, not profitable";
return None;
}

31
llvm/test/Transforms/IRCE/skip-profitability-checks.ll Normal file
View File

@ -0,0 +1,31 @@
; RUN: opt -irce-skip-profitability-checks -S -irce < %s | FileCheck %s
define void @single_access_no_preloop_no_offset(i32 *%arr, i32 *%a_len_ptr, i32 %n) {
; CHECK-LABEL: @single_access_no_preloop_no_offset(
; CHECK: main.exit.selector:
entry:
%len = load i32, i32* %a_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
br i1 %first.itr.check, label %loop, label %exit
loop:
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%abc = icmp slt i32 %idx, %len
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32, i32* %arr, i32 %idx
store i32 0, i32* %addr
%next = icmp slt i32 %idx.next, %n
br i1 %next, label %loop, label %exit
out.of.bounds:
ret void
exit:
ret void
}
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 1, i32 64}