[polly] r256123 - ScopInfo: Bail out in case of complex branch structures
Tobias Grosser via llvm-commits
llvm-commits at lists.llvm.org
Sun Dec 20 05:31:49 PST 2015
Author: grosser
Date: Sun Dec 20 07:31:48 2015
New Revision: 256123
URL: http://llvm.org/viewvc/llvm-project?rev=256123&view=rev
Log:
ScopInfo: Bail out in case of complex branch structures
Scops that contain many complex branches are likely to result in complex domain
conditions that consist of a large (> 100) number of conjucts. Transforming
such domains is expensive and unlikely to result in efficient code. To avoid
long compile times we detect this case and skip such scops. In the future we may
improve this by either using non-affine subregions to hide such complex
condition structures or by exploiting in certain cases properties (e.g.,
dominance) that allow us to construct the domains of a scop in a way that
results in a smaller number improving conjuncts.
Example of a code that results in complex iteration spaces:
loop.header
/ | \ \
A0 A2 A4 \
\ / \ / \
A1 A3 \
/ \ / \ |
B0 B2 B4 |
\ / \ / |
B1 B3 ^
/ \ / \ |
C0 C2 C4 |
\ / \ / /
C1 C3 /
\ / /
loop backedge
Added:
polly/trunk/test/ScopInfo/complex-branch-structure.ll
Modified:
polly/trunk/include/polly/ScopInfo.h
polly/trunk/lib/Analysis/ScopInfo.cpp
Modified: polly/trunk/include/polly/ScopInfo.h
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/include/polly/ScopInfo.h?rev=256123&r1=256122&r2=256123&view=diff
==============================================================================
--- polly/trunk/include/polly/ScopInfo.h (original)
+++ polly/trunk/include/polly/ScopInfo.h Sun Dec 20 07:31:48 2015
@@ -77,6 +77,7 @@ enum AssumptionKind {
INFINITELOOP,
INVARIANTLOAD,
DELINEARIZATION,
+ ERROR_DOMAINCONJUNCTS,
};
/// Maps from a loop to the affine function expressing its backedge taken count.
Modified: polly/trunk/lib/Analysis/ScopInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/ScopInfo.cpp?rev=256123&r1=256122&r2=256123&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/ScopInfo.cpp (original)
+++ polly/trunk/lib/Analysis/ScopInfo.cpp Sun Dec 20 07:31:48 2015
@@ -62,6 +62,11 @@ using namespace polly;
STATISTIC(ScopFound, "Number of valid Scops");
STATISTIC(RichScopFound, "Number of Scops containing a loop");
+// The maximal number of basic sets we allow during domain construction to
+// be created. More complex scops will result in very high compile time and
+// are also unlikely to result in good code
+static int const MaxConjunctsInDomain = 20;
+
static cl::opt<bool> ModelReadOnlyScalars(
"polly-analyze-read-only-scalars",
cl::desc("Model read-only scalar values in the scop description"),
@@ -2176,6 +2181,12 @@ void Scop::buildDomainsWithBranchConstra
SuccDomain = isl_set_union(SuccDomain, CondSet);
SuccDomain = isl_set_coalesce(SuccDomain);
+ if (isl_set_n_basic_set(SuccDomain) > MaxConjunctsInDomain) {
+ auto *Empty = isl_set_empty(isl_set_get_space(SuccDomain));
+ isl_set_free(SuccDomain);
+ SuccDomain = Empty;
+ invalidate(ERROR_DOMAINCONJUNCTS, DebugLoc());
+ }
DEBUG(dbgs() << "\tSet SuccBB: " << SuccBB->getName() << " : "
<< SuccDomain << "\n");
}
@@ -3043,6 +3054,8 @@ static std::string toString(AssumptionKi
return "Invariant load";
case DELINEARIZATION:
return "Delinearization";
+ case ERROR_DOMAINCONJUNCTS:
+ return "Low number of domain conjuncts";
}
llvm_unreachable("Unknown AssumptionKind!");
}
Added: polly/trunk/test/ScopInfo/complex-branch-structure.ll
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/ScopInfo/complex-branch-structure.ll?rev=256123&view=auto
==============================================================================
--- polly/trunk/test/ScopInfo/complex-branch-structure.ll (added)
+++ polly/trunk/test/ScopInfo/complex-branch-structure.ll Sun Dec 20 07:31:48 2015
@@ -0,0 +1,195 @@
+; RUN: opt %loadPolly -pass-remarks-analysis="polly-scops" -polly-scops \
+; RUN: < %s 2>&1 | FileCheck %s
+
+; We build a scop of the following form to check that the domain construction
+; does not take a huge amount of time, but that we instead just bail out.
+;
+; loop.header
+; / | \ \
+; A0 A2 A4 \
+; \ / \ / \
+; A1 A3 \
+; / \ / \ |
+; B0 B2 B4 |
+; \ / \ / |
+; B1 B3 ^
+; / \ / \ |
+; C0 C2 C4 |
+; \ / \ / /
+; C1 C3 /
+; \ / /
+; loop backedge
+
+; CHECK: Low number of domain conjuncts assumption: { : 1 = 0 }
+
+define void @foo(float* %A, float* %B, float* %C, float* %D, float* %E,
+ i64 %A1.p, i64 %A2.p, i64 %A3.p,
+ i64 %B1.p, i64 %B2.p, i64 %B3.p,
+ i64 %C1.p, i64 %C2.p, i64 %C3.p,
+ i64 %D1.p, i64 %D2.p, i64 %D3.p,
+ i64 %E1.p, i64 %E2.p, i64 %E3.p) {
+entry:
+ br label %loop.header
+
+loop.header:
+ %indvar = phi i64 [0, %entry], [%indvar.next, %loop.backedge]
+ switch i2 0, label %A0 [i2 1, label %A2 i2 2, label %A4]
+
+A0:
+ %val.A0 = load float, float* %A
+ store float %val.A0, float* %A
+ br label %A1
+
+A2:
+ %val.A2 = load float, float* %A
+ store float %val.A2, float* %A
+ %A2.cmp = icmp eq i64 %A2.p, 0
+ br i1 %A2.cmp, label %A1, label %A3
+
+A4:
+ %val.A4 = load float, float* %A
+ store float %val.A4, float* %A
+ br label %A3
+
+A1:
+ %val.A1 = load float, float* %A
+ store float %val.A1, float* %A
+ %A1.cmp = icmp eq i64 %A1.p, 0
+ br i1 %A1.cmp, label %B0, label %B2
+
+A3:
+ %val.A3 = load float, float* %A
+ store float %val.A3, float* %A
+ %A3.cmp = icmp eq i64 %A3.p, 0
+ br i1 %A3.cmp, label %B2, label %B4
+
+B0:
+ %val.B0 = load float, float* %B
+ store float %val.B0, float* %B
+ br label %B1
+
+B2:
+ %val.B2 = load float, float* %B
+ store float %val.B2, float* %B
+ %B2.cmp = icmp eq i64 %B2.p, 0
+ br i1 %B2.cmp, label %B1, label %B3
+
+B4:
+ %val.B4 = load float, float* %B
+ store float %val.B4, float* %B
+ br label %B3
+
+B1:
+ %val.B1 = load float, float* %B
+ store float %val.B1, float* %B
+ %B1.cmp = icmp eq i64 %B1.p, 0
+ br i1 %B1.cmp, label %C0, label %C2
+
+B3:
+ %val.B3 = load float, float* %A
+ store float %val.B3, float* %A
+ %B3.cmp = icmp eq i64 %A3.p, 0
+ br i1 %B3.cmp, label %C2, label %C4
+
+C0:
+ %val.C0 = load float, float* %C
+ store float %val.C0, float* %C
+ br label %C1
+
+C2:
+ %val.C2 = load float, float* %C
+ store float %val.C2, float* %C
+ %C2.cmp = icmp eq i64 %C2.p, 0
+ br i1 %C2.cmp, label %C1, label %C3
+
+C4:
+ %val.C4 = load float, float* %C
+ store float %val.C4, float* %C
+ br label %C3
+
+C1:
+ %val.C1 = load float, float* %C
+ store float %val.C1, float* %C
+ %C1.cmp = icmp eq i64 %C1.p, 0
+ br i1 %C1.cmp, label %D0, label %D2
+
+C3:
+ %val.C3 = load float, float* %C
+ store float %val.C3, float* %C
+ %C3.cmp = icmp eq i64 %C3.p, 0
+ br i1 %C3.cmp, label %D2, label %D4
+
+D0:
+ %val.D0 = load float, float* %D
+ store float %val.D0, float* %D
+ br label %D1
+
+D2:
+ %val.D2 = load float, float* %D
+ store float %val.D2, float* %D
+ %D2.cmp = icmp eq i64 %D2.p, 0
+ br i1 %D2.cmp, label %D1, label %D3
+
+D4:
+ %val.D4 = load float, float* %D
+ store float %val.D4, float* %D
+ br label %D3
+
+D1:
+ %val.D1 = load float, float* %D
+ store float %val.D1, float* %D
+ %D1.cmp = icmp eq i64 %D1.p, 0
+ br i1 %D1.cmp, label %E0, label %E2
+
+D3:
+ %val.D3 = load float, float* %D
+ store float %val.D3, float* %D
+ %D3.cmp = icmp eq i64 %D3.p, 0
+ br i1 %D3.cmp, label %E2, label %E4
+
+E0:
+ %val.E0 = load float, float* %E
+ store float %val.E0, float* %E
+ br label %E1
+
+E2:
+ %val.E2 = load float, float* %E
+ store float %val.E2, float* %E
+ %E2.cmp = icmp eq i64 %E2.p, 0
+ br i1 %E2.cmp, label %E1, label %E3
+
+E4:
+ %val.E4 = load float, float* %E
+ store float %val.E4, float* %E
+ br label %E3
+
+E1:
+ %val.E1 = load float, float* %E
+ store float %val.E1, float* %E
+ %E1.cmp = icmp eq i64 %E1.p, 0
+ br i1 %E1.cmp, label %F0, label %F2
+
+E3:
+ %val.E3 = load float, float* %E
+ store float %val.E3, float* %E
+ %E3.cmp = icmp eq i64 %E3.p, 0
+ br i1 %E3.cmp, label %F2, label %F4
+
+F0:
+ br label %loop.backedge
+
+F2:
+ br label %loop.backedge
+
+F4:
+ br label %loop.backedge
+
+loop.backedge:
+ %indvar.next = add i64 %indvar, 1
+ %cmp = icmp ne i64 %indvar, 1000
+ br i1 %cmp, label %loop.header, label %exit
+
+exit:
+ ret void
+
+}
More information about the llvm-commits
mailing list