[llvm] ee1c127 - [SCEV] If Start>=RHS, simplify (Start smin RHS) = RHS for trip counts.
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Mon Aug 3 09:31:26 PDT 2020
Author: Florian Hahn
Date: 2020-08-03T17:22:42+01:00
New Revision: ee1c12708a4519361729205168dedb2b61bc2638
URL: https://github.com/llvm/llvm-project/commit/ee1c12708a4519361729205168dedb2b61bc2638
DIFF: https://github.com/llvm/llvm-project/commit/ee1c12708a4519361729205168dedb2b61bc2638.diff
LOG: [SCEV] If Start>=RHS, simplify (Start smin RHS) = RHS for trip counts.
In some cases, it seems like we can get rid of unnecessary s/umins by
using information from the loop guards (unless I am missing something).
One place where this seems to be helpful in practice is when computing
loop trip counts. This patch just changes howManyGreaterThans for now.
Note that this requires a loop for which we can check 'is guarded'.
On SPEC2000/SPEC2006/MultiSource, there are some notable changes for
some programs in the number of loops unrolled and trip counts computed.
```
Same hash: 179 (filtered out)
Remaining: 58
Metric: scalar-evolution.NumTripCountsComputed
Program base patch diff
test-suite...langs-C/compiler/compiler.test 25.00 31.00 24.0%
test-suite.../Applications/SPASS/SPASS.test 2020.00 2323.00 15.0%
test-suite...langs-C/allroots/allroots.test 29.00 32.00 10.3%
test-suite.../Prolangs-C/loader/loader.test 17.00 18.00 5.9%
test-suite...fice-ispell/office-ispell.test 253.00 265.00 4.7%
test-suite...006/450.soplex/450.soplex.test 3552.00 3692.00 3.9%
test-suite...chmarks/MallocBench/gs/gs.test 453.00 470.00 3.8%
test-suite...ngs-C/assembler/assembler.test 29.00 30.00 3.4%
test-suite.../Benchmarks/Ptrdist/bc/bc.test 263.00 270.00 2.7%
test-suite...rks/FreeBench/pifft/pifft.test 722.00 741.00 2.6%
test-suite...count/automotive-bitcount.test 41.00 42.00 2.4%
test-suite...0/253.perlbmk/253.perlbmk.test 1417.00 1451.00 2.4%
test-suite...000/197.parser/197.parser.test 387.00 396.00 2.3%
test-suite...lications/sqlite3/sqlite3.test 1168.00 1189.00 1.8%
test-suite...000/255.vortex/255.vortex.test 173.00 176.00 1.7%
Metric: loop-unroll.NumUnrolled
Program base patch diff
test-suite...langs-C/compiler/compiler.test 1.00 3.00 200.0%
test-suite.../Applications/SPASS/SPASS.test 134.00 234.00 74.6%
test-suite...count/automotive-bitcount.test 3.00 4.00 33.3%
test-suite.../Prolangs-C/loader/loader.test 3.00 4.00 33.3%
test-suite...langs-C/allroots/allroots.test 3.00 4.00 33.3%
test-suite...Source/Benchmarks/sim/sim.test 10.00 12.00 20.0%
test-suite...fice-ispell/office-ispell.test 21.00 25.00 19.0%
test-suite.../Benchmarks/Ptrdist/bc/bc.test 32.00 38.00 18.8%
test-suite...006/450.soplex/450.soplex.test 300.00 352.00 17.3%
test-suite...rks/FreeBench/pifft/pifft.test 60.00 69.00 15.0%
test-suite...chmarks/MallocBench/gs/gs.test 57.00 63.00 10.5%
test-suite...ngs-C/assembler/assembler.test 10.00 11.00 10.0%
test-suite...0/253.perlbmk/253.perlbmk.test 145.00 157.00 8.3%
test-suite...000/197.parser/197.parser.test 43.00 46.00 7.0%
test-suite...TimberWolfMC/timberwolfmc.test 205.00 214.00 4.4%
Geomean difference 7.6%
```
Fixes https://bugs.llvm.org/show_bug.cgi?id=46939
Fixes https://bugs.llvm.org/show_bug.cgi?id=46924 on X86.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D85046
Added:
Modified:
llvm/lib/Analysis/ScalarEvolution.cpp
llvm/test/Analysis/ScalarEvolution/pr46939-trip-count-count-down.ll
llvm/test/Transforms/HardwareLoops/scalar-while.ll
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index a961be8cc35e..23ad77ff6054 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -10628,8 +10628,15 @@ ScalarEvolution::howManyGreaterThans(const SCEV *LHS, const SCEV *RHS,
const SCEV *Start = IV->getStart();
const SCEV *End = RHS;
- if (!isLoopEntryGuardedByCond(L, Cond, getAddExpr(Start, Stride), RHS))
- End = IsSigned ? getSMinExpr(RHS, Start) : getUMinExpr(RHS, Start);
+ if (!isLoopEntryGuardedByCond(L, Cond, getAddExpr(Start, Stride), RHS)) {
+ // If we know that Start >= RHS in the context of loop, then we know that
+ // min(RHS, Start) = RHS at this point.
+ if (isLoopEntryGuardedByCond(
+ L, IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE, Start, RHS))
+ End = RHS;
+ else
+ End = IsSigned ? getSMinExpr(RHS, Start) : getUMinExpr(RHS, Start);
+ }
const SCEV *BECount = computeBECount(getMinusSCEV(Start, End), Stride, false);
diff --git a/llvm/test/Analysis/ScalarEvolution/pr46939-trip-count-count-down.ll b/llvm/test/Analysis/ScalarEvolution/pr46939-trip-count-count-down.ll
index f1001ecec0fd..803652e47cf6 100644
--- a/llvm/test/Analysis/ScalarEvolution/pr46939-trip-count-count-down.ll
+++ b/llvm/test/Analysis/ScalarEvolution/pr46939-trip-count-count-down.ll
@@ -6,13 +6,13 @@ define void @reverse_loop(i32 %n) {
; CHECK-LABEL: 'reverse_loop'
; CHECK-NEXT: Classifying expressions for: @reverse_loop
; CHECK-NEXT: %i.011 = phi i32 [ %n, %for.body.lr.ph ], [ %dec, %for.body ]
-; CHECK-NEXT: --> {%n,+,-1}<nsw><%for.body> U: full-set S: full-set Exits: (0 smin %n) LoopDispositions: { %for.body: Computable }
+; CHECK-NEXT: --> {%n,+,-1}<nsw><%for.body> U: full-set S: full-set Exits: 0 LoopDispositions: { %for.body: Computable }
; CHECK-NEXT: %dec = add nsw i32 %i.011, -1
-; CHECK-NEXT: --> {(-1 + %n),+,-1}<nw><%for.body> U: full-set S: full-set Exits: (-1 + (0 smin %n)) LoopDispositions: { %for.body: Computable }
+; CHECK-NEXT: --> {(-1 + %n),+,-1}<nw><%for.body> U: full-set S: full-set Exits: -1 LoopDispositions: { %for.body: Computable }
; CHECK-NEXT: Determining loop execution counts for: @reverse_loop
-; CHECK-NEXT: Loop %for.body: backedge-taken count is ((-1 * (0 smin %n)) + %n)
+; CHECK-NEXT: Loop %for.body: backedge-taken count is %n
; CHECK-NEXT: Loop %for.body: max backedge-taken count is 2147483647
-; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-1 * (0 smin %n)) + %n)
+; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is %n
; CHECK-NEXT: Predicates:
; CHECK: Loop %for.body: Trip multiple is 1
;
diff --git a/llvm/test/Transforms/HardwareLoops/scalar-while.ll b/llvm/test/Transforms/HardwareLoops/scalar-while.ll
index aac94ecb8626..0b9847b33c71 100644
--- a/llvm/test/Transforms/HardwareLoops/scalar-while.ll
+++ b/llvm/test/Transforms/HardwareLoops/scalar-while.ll
@@ -76,18 +76,14 @@ while.end:
; CHECK-GUARD: br i1 %cmp4, label %while.end, label %while.body.preheader
; CHECK-GUARD: while.body.preheader:
; CHECK-GUARD: [[ADD:%[^ ]+]] = add i32 %i, 1
-; CHECK-GUARD: [[SEL:%[^ ]+]] = icmp slt i32 %N, %i
-; CHECK-GUARD: [[MIN:%[^ ]+]] = select i1 [[SEL]], i32 %N, i32 %i
-; CHECK-GUARD: [[COUNT:%[^ ]+]] = sub i32 [[ADD]], [[MIN]]
+; CHECK-GUARD: [[COUNT:%[^ ]+]] = sub i32 [[ADD]], %N
; CHECK-GUARD: call void @llvm.set.loop.iterations.i32(i32 [[COUNT]])
; CHECK-GUARD: br label %while.body
; CHECK-LABEL: while_gte
; CHECK: while.body.preheader:
; CHECK: [[ADD:%[^ ]+]] = add i32 %i, 1
-; CHECK: [[SEL:%[^ ]+]] = icmp slt i32 %N, %i
-; CHECK: [[MIN:%[^ ]+]] = select i1 [[SEL]], i32 %N, i32 %i
-; CHECK: [[COUNT:%[^ ]+]] = sub i32 [[ADD]], [[MIN]]
+; CHECK: [[COUNT:%[^ ]+]] = sub i32 [[ADD]], %N
; CHECK: call void @llvm.set.loop.iterations.i32(i32 [[COUNT]])
; CHECK: br label %while.body
More information about the llvm-commits
mailing list