[llvm] r324543 - Verify profile data confirms large loop trip counts.
Mircea Trofin via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 7 15:29:52 PST 2018
Author: mtrofin
Date: Wed Feb 7 15:29:52 2018
New Revision: 324543
URL: http://llvm.org/viewvc/llvm-project?rev=324543&view=rev
Log:
Verify profile data confirms large loop trip counts.
Summary:
Loops with inequality comparers, such as:
// unsigned bound
for (unsigned i = 1; i < bound; ++i) {...}
have getSmallConstantMaxTripCount report a large maximum static
trip count - in this case, 0xffff fffe. However, profiling info
may show that the trip count is much smaller, and thus
counter-recommend vectorization.
This change:
- flips loop-vectorize-with-block-frequency on by default.
- validates profiled loop frequency data supports vectorization,
when static info appears to not counter-recommend it. Absence
of profile data means we rely on static data, just as we've
done so far.
Reviewers: twoh, mkuper, davidxl, tejohnson, Ayal
Reviewed By: davidxl
Subscribers: bkramer, llvm-commits
Differential Revision: https://reviews.llvm.org/D42946
Modified:
llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
llvm/trunk/test/Transforms/LoopVectorize/tripcount.ll
Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=324543&r1=324542&r2=324543&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Wed Feb 7 15:29:52 2018
@@ -208,7 +208,7 @@ static cl::opt<unsigned> SmallLoopCost(
"The cost of a loop that is considered 'small' by the interleaver."));
static cl::opt<bool> LoopVectorizeWithBlockFrequency(
- "loop-vectorize-with-block-frequency", cl::init(false), cl::Hidden,
+ "loop-vectorize-with-block-frequency", cl::init(true), cl::Hidden,
cl::desc("Enable the use of the block frequency analysis to access PGO "
"heuristics minimizing code growth in cold regions and being more "
"aggressive in hot regions."));
@@ -8347,9 +8347,21 @@ bool LoopVectorizePass::processLoop(Loop
// Check the loop for a trip count threshold: vectorize loops with a tiny trip
// count by optimizing for size, to minimize overheads.
- unsigned ExpectedTC = SE->getSmallConstantMaxTripCount(L);
- bool HasExpectedTC = (ExpectedTC > 0);
-
+ // Prefer constant trip counts over profile data, over upper bound estimate.
+ unsigned ExpectedTC = 0;
+ bool HasExpectedTC = false;
+ if (const SCEVConstant *ConstExits =
+ dyn_cast<SCEVConstant>(SE->getBackedgeTakenCount(L))) {
+ const APInt &ExitsCount = ConstExits->getAPInt();
+ // We are interested in small values for ExpectedTC. Skip over those that
+ // can't fit an unsigned.
+ if (ExitsCount.ult(std::numeric_limits<unsigned>::max())) {
+ ExpectedTC = static_cast<unsigned>(ExitsCount.getZExtValue()) + 1;
+ HasExpectedTC = true;
+ }
+ }
+ // ExpectedTC may be large because it's bound by a variable. Check
+ // profiling information to validate we should vectorize.
if (!HasExpectedTC && LoopVectorizeWithBlockFrequency) {
auto EstimatedTC = getLoopEstimatedTripCount(L);
if (EstimatedTC) {
@@ -8357,6 +8369,10 @@ bool LoopVectorizePass::processLoop(Loop
HasExpectedTC = true;
}
}
+ if (!HasExpectedTC) {
+ ExpectedTC = SE->getSmallConstantMaxTripCount(L);
+ HasExpectedTC = (ExpectedTC > 0);
+ }
if (HasExpectedTC && ExpectedTC < TinyTripCountVectorThreshold) {
DEBUG(dbgs() << "LV: Found a loop with a very small trip count. "
Modified: llvm/trunk/test/Transforms/LoopVectorize/tripcount.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/tripcount.ll?rev=324543&r1=324542&r2=324543&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/tripcount.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/tripcount.ll Wed Feb 7 15:29:52 2018
@@ -57,7 +57,7 @@ for.end:
}
define i32 @foo_low_trip_count3(i1 %cond, i32 %bound) !prof !0 {
-; The loop has low invocation count compare to the function invocation count,
+; The loop has low invocation count compare to the function invocation count,
; but has a high trip count per invocation. Vectorize it.
; CHECK-LABEL: @foo_low_trip_count3(
@@ -84,6 +84,126 @@ for.end:
ret i32 0
}
+define i32 @foo_low_trip_count_icmp_sgt(i32 %bound) {
+; Simple loop with low tripcount and inequality test for exit.
+; Should not be vectorized.
+
+; CHECK-LABEL: @foo_low_trip_count_icmp_sgt(
+; CHECK-NOT: <{{[0-9]+}} x i8>
+
+entry:
+ br label %for.body
+
+for.body: ; preds = %for.body, %entry
+ %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+ %arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
+ %0 = load i8, i8* %arrayidx, align 1
+ %cmp1 = icmp eq i8 %0, 0
+ %. = select i1 %cmp1, i8 2, i8 1
+ store i8 %., i8* %arrayidx, align 1
+ %inc = add nsw i32 %i.08, 1
+ %exitcond = icmp sgt i32 %i.08, %bound
+ br i1 %exitcond, label %for.end, label %for.body, !prof !1
+
+for.end: ; preds = %for.body
+ ret i32 0
+}
+
+define i32 @const_low_trip_count() {
+; Simple loop with constant, small trip count and no profiling info.
+
+; CHECK-LABEL: @const_low_trip_count
+; CHECK-NOT: <{{[0-9]+}} x i8>
+
+entry:
+ br label %for.body
+
+for.body: ; preds = %for.body, %entry
+ %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+ %arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
+ %0 = load i8, i8* %arrayidx, align 1
+ %cmp1 = icmp eq i8 %0, 0
+ %. = select i1 %cmp1, i8 2, i8 1
+ store i8 %., i8* %arrayidx, align 1
+ %inc = add nsw i32 %i.08, 1
+ %exitcond = icmp slt i32 %i.08, 2
+ br i1 %exitcond, label %for.body, label %for.end
+
+for.end: ; preds = %for.body
+ ret i32 0
+}
+
+define i32 @const_large_trip_count() {
+; Simple loop with constant large trip count and no profiling info.
+
+; CHECK-LABEL: @const_large_trip_count
+; CHECK: <{{[0-9]+}} x i8>
+
+entry:
+ br label %for.body
+
+for.body: ; preds = %for.body, %entry
+ %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+ %arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
+ %0 = load i8, i8* %arrayidx, align 1
+ %cmp1 = icmp eq i8 %0, 0
+ %. = select i1 %cmp1, i8 2, i8 1
+ store i8 %., i8* %arrayidx, align 1
+ %inc = add nsw i32 %i.08, 1
+ %exitcond = icmp slt i32 %i.08, 1000
+ br i1 %exitcond, label %for.body, label %for.end
+
+for.end: ; preds = %for.body
+ ret i32 0
+}
+
+define i32 @const_small_trip_count_step() {
+; Simple loop with static, small trip count and no profiling info.
+
+; CHECK-LABEL: @const_small_trip_count_step
+; CHECK-NOT: <{{[0-9]+}} x i8>
+
+entry:
+ br label %for.body
+
+for.body: ; preds = %for.body, %entry
+ %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+ %arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
+ %0 = load i8, i8* %arrayidx, align 1
+ %cmp1 = icmp eq i8 %0, 0
+ %. = select i1 %cmp1, i8 2, i8 1
+ store i8 %., i8* %arrayidx, align 1
+ %inc = add nsw i32 %i.08, 5
+ %exitcond = icmp slt i32 %i.08, 10
+ br i1 %exitcond, label %for.body, label %for.end
+
+for.end: ; preds = %for.body
+ ret i32 0
+}
+
+define i32 @const_trip_over_profile() {
+; constant trip count takes precedence over profile data
+
+; CHECK-LABEL: @const_trip_over_profile
+; CHECK: <{{[0-9]+}} x i8>
+
+entry:
+ br label %for.body
+
+for.body: ; preds = %for.body, %entry
+ %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+ %arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
+ %0 = load i8, i8* %arrayidx, align 1
+ %cmp1 = icmp eq i8 %0, 0
+ %. = select i1 %cmp1, i8 2, i8 1
+ store i8 %., i8* %arrayidx, align 1
+ %inc = add nsw i32 %i.08, 1
+ %exitcond = icmp slt i32 %i.08, 1000
+ br i1 %exitcond, label %for.body, label %for.end, !prof !1
+
+for.end: ; preds = %for.body
+ ret i32 0
+}
!0 = !{!"function_entry_count", i64 100}
!1 = !{!"branch_weights", i32 100, i32 0}
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