[llvm] 0861900 - [SCEV] Avoid compile time explosion in ScalarEvolution::isImpliedCond
Bjorn Pettersson via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 19 12:39:27 PDT 2021
Author: Bjorn Pettersson
Date: 2021-10-19T21:37:57+02:00
New Revision: 08619006a0c0694477f143dc1552eab35701e50b
URL: https://github.com/llvm/llvm-project/commit/08619006a0c0694477f143dc1552eab35701e50b
DIFF: https://github.com/llvm/llvm-project/commit/08619006a0c0694477f143dc1552eab35701e50b.diff
LOG: [SCEV] Avoid compile time explosion in ScalarEvolution::isImpliedCond
As seen in PR51869 the ScalarEvolution::isImpliedCond function might
end up spending lots of time when doing the isKnownPredicate checks.
Calling isKnownPredicate for example result in isKnownViaInduction
being called, which might result in isLoopBackedgeGuardedByCond being
called, and then we might get one or more new calls to isImpliedCond.
Even if the scenario described here isn't an infinite loop, using
some random generated C programs as input indicates that those
isKnownPredicate checks quite often returns true. On the other hand,
the third condition that needs to be fulfilled in order to "prove
implications via truncation", i.e. the isImpliedCondBalancedTypes
check, is rarely fulfilled.
I also made some similar experiments to look at how often we would
get the same result when using isKnownViaNonRecursiveReasoning instead
of isKnownPredicate. So far I haven't seen a single case when codegen
is negatively impacted by using isKnownViaNonRecursiveReasoning. On
the other hand, it seems like we get rid of the compile time explosion
seen in PR51869 that way. Hence this patch.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D112080
Added:
llvm/test/Analysis/ScalarEvolution/pr51869-scalar-evolution-prove-implications-via-truncation.ll
Modified:
llvm/lib/Analysis/ScalarEvolution.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index f022052f4530d..33e512710966f 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -10669,8 +10669,8 @@ bool ScalarEvolution::isImpliedCond(ICmpInst::Predicate Pred, const SCEV *LHS,
auto BitWidth = getTypeSizeInBits(NarrowType);
const SCEV *MaxValue = getZeroExtendExpr(
getConstant(APInt::getMaxValue(BitWidth)), WideType);
- if (isKnownPredicate(ICmpInst::ICMP_ULE, FoundLHS, MaxValue) &&
- isKnownPredicate(ICmpInst::ICMP_ULE, FoundRHS, MaxValue)) {
+ if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, FoundLHS, MaxValue) &&
+ isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, FoundRHS, MaxValue)) {
const SCEV *TruncFoundLHS = getTruncateExpr(FoundLHS, NarrowType);
const SCEV *TruncFoundRHS = getTruncateExpr(FoundRHS, NarrowType);
if (isImpliedCondBalancedTypes(Pred, LHS, RHS, FoundPred, TruncFoundLHS,
diff --git a/llvm/test/Analysis/ScalarEvolution/pr51869-scalar-evolution-prove-implications-via-truncation.ll b/llvm/test/Analysis/ScalarEvolution/pr51869-scalar-evolution-prove-implications-via-truncation.ll
new file mode 100644
index 0000000000000..ec732ec3d38d9
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/pr51869-scalar-evolution-prove-implications-via-truncation.ll
@@ -0,0 +1,218 @@
+; RUN: opt < %s -disable-output -passes=indvars
+
+; Do not timeout (and do not crash).
+;
+; This test case used to take around 10 minutes to run (well, that of course
+; depends on which kind of build that is used and on which kind of server the
+; test is executed). There is a less reduced version of this test case in
+; PR51869 that takes much longer time to execute (I've not seen that one
+; terminate within reasonable time). Maybe this test case is reduced a bit too
+; much if being considered as a regression tests that would timeout without
+; the fix. It can at least be used to show compile time explosion that
+; happened when using isKnownPredicate inside ScalarEvolution::isImpliedCond.
+
+ at v_228 = external dso_local global i32, align 1
+
+; Function Attrs: nounwind
+define dso_local i16 @main(i16* %0, i16* %1, i16* %2, i16* %3, i16* %4, i16* %5, i16* %6, i16* %7, i16* %8, i16* %9, i16* %10, i1 %11) #0 {
+ br i1 %11, label %27, label %13
+
+13: ; preds = %12
+ %14 = load i32, i32* @v_228, align 1
+ %15 = trunc i32 %14 to i16
+ %16 = mul i16 %15, 2
+ %17 = sub i16 10, %16
+ %18 = icmp ult i16 10, %16
+ %19 = icmp ult i16 %17, 1
+ %20 = or i1 %18, %19
+ br i1 %20, label %139, label %21
+
+21: ; preds = %13
+ %22 = add i16 %16, 1
+ %23 = sub i16 10, %22
+ %24 = icmp ult i16 10, %22
+ %25 = icmp ult i16 %23, 1
+ %26 = or i1 %24, %25
+ br i1 %26, label %139, label %27
+
+27: ; preds = %21, %12
+ %28 = load i16, i16* %1, align 1
+ br label %29
+
+29: ; preds = %29, %27
+ %30 = phi i16 [ %28, %27 ], [ %31, %29 ]
+ %31 = add i16 %30, 1
+ %32 = icmp slt i16 %31, 28
+ br i1 %32, label %29, label %33
+
+33: ; preds = %29
+ %34 = load i16, i16* %2, align 1
+ br label %35
+
+35: ; preds = %43, %33
+ %36 = phi i16 [ %34, %33 ], [ %44, %43 ]
+ %37 = sext i16 %36 to i32
+ %38 = mul i32 %37, 2
+ %39 = sub i32 56, %38
+ %40 = icmp ult i32 56, %38
+ %41 = icmp ult i32 %39, 2
+ %42 = or i1 %40, %41
+ br i1 %42, label %139, label %43
+
+43: ; preds = %35
+ %44 = add i16 %36, 1
+ %45 = icmp slt i16 %44, 28
+ br i1 %45, label %35, label %46
+
+46: ; preds = %43
+ %47 = load i16, i16* %3, align 1
+ br label %48
+
+48: ; preds = %55, %46
+ %49 = phi i16 [ %47, %46 ], [ %56, %55 ]
+ %50 = mul i16 %49, 4
+ %51 = sub i16 28, %50
+ %52 = icmp ult i16 28, %50
+ %53 = icmp ult i16 %51, 4
+ %54 = or i1 %52, %53
+ br i1 %54, label %139, label %55
+
+55: ; preds = %48
+ %56 = add i16 %49, 1
+ %57 = icmp slt i16 %56, 7
+ br i1 %57, label %48, label %58
+
+58: ; preds = %55
+ %59 = load i16, i16* %4, align 1
+ br label %60
+
+60: ; preds = %67, %58
+ %61 = phi i16 [ %59, %58 ], [ %68, %67 ]
+ %62 = sext i16 %61 to i32
+ %63 = sub i32 1, %62
+ %64 = icmp ult i32 1, %62
+ %65 = icmp ult i32 %63, 1
+ %66 = or i1 %64, %65
+ br i1 %66, label %139, label %67
+
+67: ; preds = %60
+ %68 = add i16 %61, 1
+ %69 = icmp slt i16 %68, 1
+ br i1 %69, label %60, label %70
+
+70: ; preds = %67
+ %71 = load i16, i16* %5, align 1
+ br label %72
+
+72: ; preds = %79, %70
+ %73 = phi i16 [ %71, %70 ], [ %80, %79 ]
+ %74 = sext i16 %73 to i32
+ %75 = sub i32 1, %74
+ %76 = icmp ult i32 1, %74
+ %77 = icmp ult i32 %75, 1
+ %78 = or i1 %76, %77
+ br i1 %78, label %139, label %79
+
+79: ; preds = %72
+ %80 = add i16 %73, 1
+ %81 = icmp slt i16 %80, 1
+ br i1 %81, label %72, label %82
+
+82: ; preds = %79
+ %83 = load i16, i16* %6, align 1
+ br label %84
+
+84: ; preds = %91, %82
+ %85 = phi i16 [ %83, %82 ], [ %92, %91 ]
+ %86 = sext i16 %85 to i32
+ %87 = sub i32 1, %86
+ %88 = icmp ult i32 1, %86
+ %89 = icmp ult i32 %87, 1
+ %90 = or i1 %88, %89
+ br i1 %90, label %139, label %91
+
+91: ; preds = %84
+ %92 = add i16 %85, 1
+ %93 = icmp slt i16 %92, 1
+ br i1 %93, label %84, label %94
+
+94: ; preds = %91
+ %95 = load i16, i16* %7, align 1
+ br label %96
+
+96: ; preds = %103, %94
+ %97 = phi i16 [ %95, %94 ], [ %104, %103 ]
+ %98 = sext i16 %97 to i32
+ %99 = sub i32 1, %98
+ %100 = icmp ult i32 1, %98
+ %101 = icmp ult i32 %99, 1
+ %102 = or i1 %100, %101
+ br i1 %102, label %139, label %103
+
+103: ; preds = %96
+ %104 = add i16 %97, 1
+ %105 = icmp slt i16 %104, 1
+ br i1 %105, label %96, label %106
+
+106: ; preds = %103
+ %107 = load i16, i16* %8, align 1
+ br label %108
+
+108: ; preds = %115, %106
+ %109 = phi i16 [ %107, %106 ], [ %116, %115 ]
+ %110 = mul i16 %109, 4
+ %111 = sub i16 24, %110
+ %112 = icmp ult i16 24, %110
+ %113 = icmp ult i16 %111, 4
+ %114 = or i1 %112, %113
+ br i1 %114, label %139, label %115
+
+115: ; preds = %108
+ %116 = add i16 %109, 1
+ %117 = icmp slt i16 %116, 6
+ br i1 %117, label %108, label %118
+
+118: ; preds = %115
+ %119 = load i16, i16* %9, align 1
+ br label %120
+
+120: ; preds = %128, %118
+ %121 = phi i16 [ %119, %118 ], [ %129, %128 ]
+ %122 = sext i16 %121 to i32
+ %123 = mul i32 %122, 2
+ %124 = sub i32 4, %123
+ %125 = icmp ult i32 4, %123
+ %126 = icmp ult i32 %124, 2
+ %127 = or i1 %125, %126
+ br i1 %127, label %139, label %128
+
+128: ; preds = %120
+ %129 = add i16 %121, 1
+ %130 = icmp slt i16 %129, 2
+ br i1 %130, label %120, label %131
+
+131: ; preds = %128
+ %132 = load i16, i16* %10, align 1
+ br label %133
+
+133: ; preds = %133, %131
+ %134 = phi i16 [ %132, %131 ], [ %135, %133 ]
+ %135 = add i16 %134, 1
+ %136 = icmp slt i16 %135, 6
+ br i1 %136, label %133, label %137
+
+137: ; preds = %133
+ %138 = load i16, i16* %0, align 1
+ ret i16 %138
+
+139: ; preds = %120, %108, %96, %84, %72, %60, %48, %35, %21, %13
+ call void @llvm.trap() #2
+ unreachable
+}
+
+; Function Attrs: cold noreturn nounwind
+declare void @llvm.trap() #1
+
+attributes #0 = { nounwind }
+attributes #1 = { cold noreturn nounwind }
+attributes #2 = { noreturn nounwind }
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