[llvm-commits] [llvm] r144746 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll test/Transforms/IndVarSimplify/loop_evaluate10.ll test/Transforms/IndVarSimplify/loop_evaluate9.ll
Andrew Trick
atrick at apple.com
Tue Nov 15 16:52:40 PST 2011
Author: atrick
Date: Tue Nov 15 18:52:40 2011
New Revision: 144746
URL: http://llvm.org/viewvc/llvm-project?rev=144746&view=rev
Log:
Fix SCEV overly optimistic back edge taken count for multi-exit loops.
Fixes PR11375: Different results for 'clang++ huh.cpp'...
Added:
llvm/trunk/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll
Modified:
llvm/trunk/lib/Analysis/ScalarEvolution.cpp
llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate10.ll
llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate9.ll
Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=144746&r1=144745&r2=144746&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Tue Nov 15 18:52:40 2011
@@ -4153,13 +4153,19 @@
}
/// getExact - Get the exact loop backedge taken count considering all loop
-/// exits. If all exits are computable, this is the minimum computed count.
+/// exits. A computable result can only be return for loops with a single exit.
+/// Returning the minimum taken count among all exits is incorrect because one
+/// of the loop's exit limit's may have been skipped. HowFarToZero assumes that
+/// the limit of each loop test is never skipped. This is a valid assumption as
+/// long as the loop exits via that test. For precise results, it is the
+/// caller's responsibility to specify the relevant loop exit using
+/// getExact(ExitingBlock, SE).
const SCEV *
ScalarEvolution::BackedgeTakenInfo::getExact(ScalarEvolution *SE) const {
// If any exits were not computable, the loop is not computable.
if (!ExitNotTaken.isCompleteList()) return SE->getCouldNotCompute();
- // We need at least one computable exit.
+ // We need exactly one computable exit.
if (!ExitNotTaken.ExitingBlock) return SE->getCouldNotCompute();
assert(ExitNotTaken.ExactNotTaken && "uninitialized not-taken info");
@@ -4171,8 +4177,8 @@
if (!BECount)
BECount = ENT->ExactNotTaken;
- else
- BECount = SE->getUMinFromMismatchedTypes(BECount, ENT->ExactNotTaken);
+ else if (BECount != ENT->ExactNotTaken)
+ return SE->getCouldNotCompute();
}
assert(BECount && "Invalid not taken count for loop exit");
return BECount;
@@ -4253,8 +4259,15 @@
if (MaxBECount == getCouldNotCompute())
MaxBECount = EL.Max;
- else if (EL.Max != getCouldNotCompute())
- MaxBECount = getUMinFromMismatchedTypes(MaxBECount, EL.Max);
+ else if (EL.Max != getCouldNotCompute()) {
+ // We cannot take the "min" MaxBECount, because non-unit stride loops may
+ // skip some loop tests. Taking the max over the exits is sufficiently
+ // conservative. TODO: We could do better taking into consideration
+ // that (1) the loop has unit stride (2) the last loop test is
+ // less-than/greater-than (3) any loop test is less-than/greater-than AND
+ // falls-through some constant times less then the other tests.
+ MaxBECount = getUMaxFromMismatchedTypes(MaxBECount, EL.Max);
+ }
}
return BackedgeTakenInfo(ExitCounts, CouldComputeBECount, MaxBECount);
@@ -4920,7 +4933,7 @@
// the loop symbolically to determine when the condition gets a value of
// "ExitWhen".
- unsigned MaxIterations = MaxBruteForceIterations; // Limit analysis.
+ unsigned MaxIterations = MaxBruteForceIterations; // Limit analysis.
for (unsigned IterationNum = 0; IterationNum != MaxIterations;++IterationNum){
ConstantInt *CondVal =
dyn_cast_or_null<ConstantInt>(EvaluateExpression(Cond, L,
@@ -5507,10 +5520,10 @@
// behavior. Loops must exhibit defined behavior until a wrapped value is
// actually used. So the trip count computed by udiv could be smaller than the
// number of well-defined iterations.
- if (AddRec->getNoWrapFlags(SCEV::FlagNW))
+ if (AddRec->getNoWrapFlags(SCEV::FlagNW)) {
// FIXME: We really want an "isexact" bit for udiv.
return getUDivExpr(Distance, CountDown ? getNegativeSCEV(Step) : Step);
-
+ }
// Then, try to solve the above equation provided that Start is constant.
if (const SCEVConstant *StartC = dyn_cast<SCEVConstant>(Start))
return SolveLinEquationWithOverflow(StepC->getValue()->getValue(),
Added: llvm/trunk/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll?rev=144746&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll (added)
+++ llvm/trunk/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll Tue Nov 15 18:52:40 2011
@@ -0,0 +1,40 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+;
+; Prior to the fix for PR11375, indvars would replace %firstIV with a
+; loop-invariant gep computed in the preheader. This was incorrect
+; because it was based on the minimum "ExitNotTaken" count. If the
+; final loop test is skipped (odd number of elements) then the early
+; exit would be taken and the loop invariant value would be incorrect.
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-darwin"
+
+; CHECK: if.end:
+; CHECK: phi i32* [ %first.lcssa, %early.exit ]
+define i32 @test(i32* %first, i32* %last) uwtable ssp {
+entry:
+ br i1 undef, label %if.end, label %if.then
+
+if.then: ; preds = %entry
+ br i1 undef, label %if.end, label %do.body
+
+do.body: ; preds = %if.else, %if.then
+ %firstIV = phi i32* [ %incdec.ptr2, %if.else ], [ %first, %if.then ]
+ %incdec.ptr1 = getelementptr inbounds i32* %firstIV, i64 1
+ %cmp1 = icmp eq i32* %incdec.ptr1, %last
+ br i1 %cmp1, label %early.exit, label %if.else
+
+if.else: ; preds = %do.body
+ %incdec.ptr2 = getelementptr inbounds i32* %firstIV, i64 2
+ %cmp2 = icmp eq i32* %incdec.ptr2, %last
+ br i1 %cmp2, label %if.end, label %do.body
+
+early.exit:
+ %first.lcssa = phi i32* [ %firstIV, %do.body ]
+ br label %if.end
+
+if.end:
+ %tmp = phi i32* [ %first.lcssa, %early.exit ], [ %first, %if.then ], [ %first, %entry ], [ undef, %if.else ]
+ %val = load i32* %tmp
+ ret i32 %val
+}
Modified: llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate10.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate10.ll?rev=144746&r1=144745&r2=144746&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate10.ll (original)
+++ llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate10.ll Tue Nov 15 18:52:40 2011
@@ -1,8 +1,14 @@
; RUN: opt < %s -indvars -S \
; RUN: | grep {%b.1 = phi i32 \\\[ 2, %bb \\\], \\\[ 1, %bb2 \\\]}
-
+;
; This loop has multiple exits, and the value of %b1 depends on which
; exit is taken. Indvars should correctly compute the exit values.
+;
+; XFAIL: *
+; Indvars does not currently replace loop invariant values unless all
+; loop exits have the same exit value. We could handle some cases,
+; such as this, by making getSCEVAtScope() sensitive to a particular
+; loop exit. See PR11388.
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-pc-linux-gnu"
Modified: llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate9.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate9.ll?rev=144746&r1=144745&r2=144746&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate9.ll (original)
+++ llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate9.ll Tue Nov 15 18:52:40 2011
@@ -2,8 +2,13 @@
; RUN: grep {\[%\]tmp7 = icmp eq i8 -28, -28} %t
; RUN: grep {\[%\]tmp8 = icmp eq i8 63, 63} %t
; PR4477
-
; Indvars should compute the exit values in loop.
+;
+; XFAIL: *
+; Indvars does not currently replace loop invariant values unless all
+; loop exits have the same exit value. We could handle some cases,
+; such as this, by making getSCEVAtScope() sensitive to a particular
+; loop exit. See PR11388.
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
target triple = "i386-pc-linux-gnu"
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