[llvm] 400f6ed - [IRCE] Use the same min runtime iteration threshold for BPI and BFI checks

[Serguei Katkov via llvm-commits]

Author: Serguei Katkov
Date: 2020-11-16T09:21:50+07:00
New Revision: 400f6edce7541e071afe18e40cca745a672e84dc

URL: https://github.com/llvm/llvm-project/commit/400f6edce7541e071afe18e40cca745a672e84dc
DIFF: https://github.com/llvm/llvm-project/commit/400f6edce7541e071afe18e40cca745a672e84dc.diff

LOG: [IRCE] Use the same min runtime iteration threshold for BPI and BFI checks

In the last change to IRCE the BPI is ignored if BFI is present, however
BFI and BPI have a different thresholds. Specifically BPI approach checks only
latch exit probability so it is expected if the loop has only one exit block (latch)
the behavior with BFI and BPI should be the same,

BPI approach by default uses threshold 10, so it considers the loop with estimated
number of iterations less then 10 should not be considered for IRCE optimization.
BFI approach uses the default value 3 and this is inconsistent.

The CL modifies the code to use the same threshold for both approaches..

The test is updated due to it has two side-exits (except latch) and each of them has a
probability 1/16, so BFI estimates the number of runtime iteration is about to 7
(1/16 + 1/16 + some for latch) and test fails.

Reviewers: mkazantsev, ebrevnov
Reviewed By: mkazantsev
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D91230

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
    llvm/test/Transforms/IRCE/low-iterations.ll
    llvm/test/Transforms/IRCE/multiple-access-no-preloop.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index ef5ea30ffeac..12e86e0ea920 100644
--- a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -110,14 +110,11 @@ static cl::opt<bool> PrintChangedLoops("irce-print-changed-loops", cl::Hidden,
 static cl::opt<bool> PrintRangeChecks("irce-print-range-checks", cl::Hidden,
                                       cl::init(false));
 
-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));
 
-static cl::opt<unsigned> MinRuntimeIterations("min-runtime-iterations",
-                                              cl::Hidden, cl::init(3));
+static cl::opt<unsigned> MinRuntimeIterations("irce-min-runtime-iterations",
+                                              cl::Hidden, cl::init(10));
 
 static cl::opt<bool> AllowUnsignedLatchCondition("irce-allow-unsigned-latch",
                                                  cl::Hidden, cl::init(true));
@@ -1871,7 +1868,7 @@ InductiveRangeCheckElimination::isProfitableToTransform(const Loop &L,
     return true;
   BranchProbability ExitProbability =
       BPI->getEdgeProbability(LS.Latch, LS.LatchBrExitIdx);
-  if (ExitProbability > BranchProbability(1, MaxExitProbReciprocal)) {
+  if (ExitProbability > BranchProbability(1, MinRuntimeIterations)) {
     LLVM_DEBUG(dbgs() << "irce: could not prove profitability: "
                       << "the exit probability is too big " << ExitProbability
                       << "\n";);

diff  --git a/llvm/test/Transforms/IRCE/low-iterations.ll b/llvm/test/Transforms/IRCE/low-iterations.ll
index 4d174e9fcbc6..7a82852fe883 100644
--- a/llvm/test/Transforms/IRCE/low-iterations.ll
+++ b/llvm/test/Transforms/IRCE/low-iterations.ll
@@ -1,5 +1,5 @@
-; RUN: opt -verify-loop-info -irce-print-changed-loops -passes=irce -min-runtime-iterations=3 < %s 2>&1 | FileCheck %s --check-prefixes=CHECK-NO
-; RUN: opt -verify-loop-info -irce-print-changed-loops -passes=irce -min-runtime-iterations=0 < %s 2>&1 | FileCheck %s --check-prefixes=CHECK-YES
+; RUN: opt -verify-loop-info -irce-print-changed-loops -passes=irce -irce-min-runtime-iterations=3 < %s 2>&1 | FileCheck %s --check-prefixes=CHECK-NO
+; RUN: opt -verify-loop-info -irce-print-changed-loops -passes=irce -irce-min-runtime-iterations=0 < %s 2>&1 | FileCheck %s --check-prefixes=CHECK-YES
 
 ; CHECK-YES: constrained Loop
 ; CHECK-NO-NOT: constrained Loop

diff  --git a/llvm/test/Transforms/IRCE/multiple-access-no-preloop.ll b/llvm/test/Transforms/IRCE/multiple-access-no-preloop.ll
index 7ef305b0569e..2abbe4146e07 100644
--- a/llvm/test/Transforms/IRCE/multiple-access-no-preloop.ll
+++ b/llvm/test/Transforms/IRCE/multiple-access-no-preloop.ll
@@ -60,4 +60,4 @@ define void @multiple_access_no_preloop(
 ; CHECK: br i1 %next.postloop, label %loop.postloop, label %exit.loopexit
 
 !0 = !{i32 0, i32 2147483647}
-!1 = !{!"branch_weights", i32 64, i32 4}
+!1 = !{!"branch_weights", i32 128, i32 4}