[llvm-commits] [llvm] r73862 - in /llvm/trunk: include/llvm/Analysis/ScalarEvolution.h lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll test/Analysis/ScalarEvolution/trip-count3.ll test/Transforms/IndVarSimplify/loop_evaluate_6.ll
Dan Gohman
gohman at apple.com
Sun Jun 21 16:46:39 PDT 2009
Author: djg
Date: Sun Jun 21 18:46:38 2009
New Revision: 73862
URL: http://llvm.org/viewvc/llvm-project?rev=73862&view=rev
Log:
Fix ScalarEvolution's backedge-taken count computations to check for
overflow when computing a integer division to round up.
Thanks to Nick Lewycky for noticing this!
Modified:
llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
llvm/trunk/lib/Analysis/ScalarEvolution.cpp
llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll
llvm/trunk/test/Analysis/ScalarEvolution/trip-count3.ll
llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate_6.ll
Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ScalarEvolution.h?rev=73862&r1=73861&r2=73862&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
+++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Sun Jun 21 18:46:38 2009
@@ -332,6 +332,13 @@
const SCEVHandle &SymName,
const SCEVHandle &NewVal);
+ /// getBECount - Subtract the end and start values and divide by the step,
+ /// rounding up, to get the number of times the backedge is executed. Return
+ /// CouldNotCompute if an intermediate computation overflows.
+ SCEVHandle getBECount(const SCEVHandle &Start,
+ const SCEVHandle &End,
+ const SCEVHandle &Step);
+
/// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given
/// loop, lazily computing new values if the loop hasn't been analyzed
/// yet.
Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=73862&r1=73861&r2=73862&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Sun Jun 21 18:46:38 2009
@@ -3788,6 +3788,33 @@
return false;
}
+/// getBECount - Subtract the end and start values and divide by the step,
+/// rounding up, to get the number of times the backedge is executed. Return
+/// CouldNotCompute if an intermediate computation overflows.
+SCEVHandle ScalarEvolution::getBECount(const SCEVHandle &Start,
+ const SCEVHandle &End,
+ const SCEVHandle &Step) {
+ const Type *Ty = Start->getType();
+ SCEVHandle NegOne = getIntegerSCEV(-1, Ty);
+ SCEVHandle Diff = getMinusSCEV(End, Start);
+ SCEVHandle RoundUp = getAddExpr(Step, NegOne);
+
+ // Add an adjustment to the difference between End and Start so that
+ // the division will effectively round up.
+ SCEVHandle Add = getAddExpr(Diff, RoundUp);
+
+ // Check Add for unsigned overflow.
+ // TODO: More sophisticated things could be done here.
+ const Type *WideTy = IntegerType::get(getTypeSizeInBits(Ty) + 1);
+ SCEVHandle OperandExtendedAdd =
+ getAddExpr(getZeroExtendExpr(Diff, WideTy),
+ getZeroExtendExpr(RoundUp, WideTy));
+ if (getZeroExtendExpr(Add, WideTy) != OperandExtendedAdd)
+ return CouldNotCompute;
+
+ return getUDivExpr(Add, Step);
+}
+
/// HowManyLessThans - Return the number of times a backedge containing the
/// specified less-than comparison will execute. If not computable, return
/// CouldNotCompute.
@@ -3869,16 +3896,11 @@
// Finally, we subtract these two values and divide, rounding up, to get
// the number of times the backedge is executed.
- SCEVHandle BECount = getUDivExpr(getAddExpr(getMinusSCEV(End, Start),
- getAddExpr(Step, NegOne)),
- Step);
+ SCEVHandle BECount = getBECount(Start, End, Step);
// The maximum backedge count is similar, except using the minimum start
// value and the maximum end value.
- SCEVHandle MaxBECount = getUDivExpr(getAddExpr(getMinusSCEV(MaxEnd,
- MinStart),
- getAddExpr(Step, NegOne)),
- Step);
+ SCEVHandle MaxBECount = getBECount(MinStart, MaxEnd, Step);;
return BackedgeTakenInfo(BECount, MaxBECount);
}
Modified: llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll?rev=73862&r1=73861&r2=73862&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll Sun Jun 21 18:46:38 2009
@@ -1,4 +1,9 @@
-; RUN: llvm-as < %s | opt -analyze -scalar-evolution -disable-output |& grep {/u 3}
+; RUN: llvm-as < %s | opt -analyze -scalar-evolution -disable-output \
+; RUN: | grep {Loop bb: Unpredictable backedge-taken count\\.}
+
+; ScalarEvolution can't compute a trip count because it doesn't know if
+; dividing by the stride will have a remainder. This could theoretically
+; be teaching it how to use a more elaborate trip count computation.
define i32 @f(i32 %x) nounwind readnone {
entry:
Modified: llvm/trunk/test/Analysis/ScalarEvolution/trip-count3.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/trip-count3.ll?rev=73862&r1=73861&r2=73862&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/trip-count3.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/trip-count3.ll Sun Jun 21 18:46:38 2009
@@ -1,5 +1,9 @@
; RUN: llvm-as < %s | opt -scalar-evolution -analyze -disable-output \
-; RUN: | grep {backedge-taken count is ((64 + (-64 smax (-1 + (-1 \\* %0))) + %0) /u 64)}
+; RUN: | grep {Loop bb3\\.i: Unpredictable backedge-taken count\\.}
+
+; ScalarEvolution can't compute a trip count because it doesn't know if
+; dividing by the stride will have a remainder. This could theoretically
+; be teaching it how to use a more elaborate trip count computation.
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-unknown-linux-gnu"
Modified: llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate_6.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate_6.ll?rev=73862&r1=73861&r2=73862&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate_6.ll (original)
+++ llvm/trunk/test/Transforms/IndVarSimplify/loop_evaluate_6.ll Sun Jun 21 18:46:38 2009
@@ -1,7 +1,9 @@
; RUN: llvm-as < %s | opt -indvars -loop-deletion | llvm-dis | grep phi | count 1
+; XFAIL: *
-; Indvars should be able to evaluate this loop, allowing loop deletion
-; to delete it.
+; Indvars can't evaluate this loop, because ScalarEvolution can't compute
+; an exact trip count, because it doesn't know if dividing by the stride will
+; have a remainder. It could be done with more aggressive VRP though.
define i32 @test(i32 %x_offs) nounwind readnone {
entry:
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