[llvm] r276372 - [IRCE] Add an option to skip profitability checks

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Thu Jul 21 19:40:56 2016
New Revision: 276372

URL: http://llvm.org/viewvc/llvm-project?rev=276372&view=rev
Log:
[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.

Added:
    llvm/trunk/test/Transforms/IRCE/skip-profitability-checks.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp?rev=276372&r1=276371&r2=276372&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp Thu Jul 21 19:40:56 2016
@@ -82,6 +82,9 @@ static cl::opt<bool> PrintRangeChecks("i
 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::extractRangeCh
 
   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(Scalar
   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;
   }

Added: llvm/trunk/test/Transforms/IRCE/skip-profitability-checks.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IRCE/skip-profitability-checks.ll?rev=276372&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IRCE/skip-profitability-checks.ll (added)
+++ llvm/trunk/test/Transforms/IRCE/skip-profitability-checks.ll Thu Jul 21 19:40:56 2016
@@ -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}