[llvm-commits] [llvm] r82151 - in /llvm/trunk: include/llvm/Analysis/ScalarEvolution.h lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/nsw-offset.ll
Dan Gohman
gohman at apple.com
Thu Sep 17 11:05:21 PDT 2009
Author: djg
Date: Thu Sep 17 13:05:20 2009
New Revision: 82151
URL: http://llvm.org/viewvc/llvm-project?rev=82151&view=rev
Log:
Teach ScalarEvolution how to reason about no-wrap flags on loops
where the induction variable has a non-unit stride, such as {0,+,2}, and
there are expressions such as {1,+,2} inside the loop formed with
or or add nsw operators.
Added:
llvm/trunk/test/Analysis/ScalarEvolution/nsw-offset.ll
Modified:
llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
llvm/trunk/lib/Analysis/ScalarEvolution.cpp
Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ScalarEvolution.h?rev=82151&r1=82150&r2=82151&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
+++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Thu Sep 17 13:05:20 2009
@@ -253,7 +253,8 @@
/// CouldNotCompute if an intermediate computation overflows.
const SCEV *getBECount(const SCEV *Start,
const SCEV *End,
- const SCEV *Step);
+ const SCEV *Step,
+ bool NoWrap);
/// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given
/// loop, lazily computing new values if the loop hasn't been analyzed
Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=82151&r1=82150&r2=82151&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Thu Sep 17 13:05:20 2009
@@ -2972,8 +2972,20 @@
const SCEV *LHS = getSCEV(U->getOperand(0));
const APInt &CIVal = CI->getValue();
if (GetMinTrailingZeros(LHS) >=
- (CIVal.getBitWidth() - CIVal.countLeadingZeros()))
- return getAddExpr(LHS, getSCEV(U->getOperand(1)));
+ (CIVal.getBitWidth() - CIVal.countLeadingZeros())) {
+ // Build a plain add SCEV.
+ const SCEV *S = getAddExpr(LHS, getSCEV(CI));
+ // If the LHS of the add was an addrec and it has no-wrap flags,
+ // transfer the no-wrap flags, since an or won't introduce a wrap.
+ if (const SCEVAddRecExpr *NewAR = dyn_cast<SCEVAddRecExpr>(S)) {
+ const SCEVAddRecExpr *OldAR = cast<SCEVAddRecExpr>(LHS);
+ if (OldAR->hasNoUnsignedWrap())
+ const_cast<SCEVAddRecExpr *>(NewAR)->setHasNoUnsignedWrap(true);
+ if (OldAR->hasNoSignedWrap())
+ const_cast<SCEVAddRecExpr *>(NewAR)->setHasNoSignedWrap(true);
+ }
+ return S;
+ }
}
break;
case Instruction::Xor:
@@ -4795,7 +4807,8 @@
/// CouldNotCompute if an intermediate computation overflows.
const SCEV *ScalarEvolution::getBECount(const SCEV *Start,
const SCEV *End,
- const SCEV *Step) {
+ const SCEV *Step,
+ bool NoWrap) {
const Type *Ty = Start->getType();
const SCEV *NegOne = getIntegerSCEV(-1, Ty);
const SCEV *Diff = getMinusSCEV(End, Start);
@@ -4805,15 +4818,17 @@
// the division will effectively round up.
const SCEV *Add = getAddExpr(Diff, RoundUp);
- // Check Add for unsigned overflow.
- // TODO: More sophisticated things could be done here.
- const Type *WideTy = IntegerType::get(getContext(),
- getTypeSizeInBits(Ty) + 1);
- const SCEV *EDiff = getZeroExtendExpr(Diff, WideTy);
- const SCEV *ERoundUp = getZeroExtendExpr(RoundUp, WideTy);
- const SCEV *OperandExtendedAdd = getAddExpr(EDiff, ERoundUp);
- if (getZeroExtendExpr(Add, WideTy) != OperandExtendedAdd)
- return getCouldNotCompute();
+ if (!NoWrap) {
+ // Check Add for unsigned overflow.
+ // TODO: More sophisticated things could be done here.
+ const Type *WideTy = IntegerType::get(getContext(),
+ getTypeSizeInBits(Ty) + 1);
+ const SCEV *EDiff = getZeroExtendExpr(Diff, WideTy);
+ const SCEV *ERoundUp = getZeroExtendExpr(RoundUp, WideTy);
+ const SCEV *OperandExtendedAdd = getAddExpr(EDiff, ERoundUp);
+ if (getZeroExtendExpr(Add, WideTy) != OperandExtendedAdd)
+ return getCouldNotCompute();
+ }
return getUDivExpr(Add, Step);
}
@@ -4831,6 +4846,10 @@
if (!AddRec || AddRec->getLoop() != L)
return getCouldNotCompute();
+ // Check to see if we have a flag which makes analysis easy.
+ bool NoWrap = isSigned ? AddRec->hasNoSignedWrap() :
+ AddRec->hasNoUnsignedWrap();
+
if (AddRec->isAffine()) {
// FORNOW: We only support unit strides.
unsigned BitWidth = getTypeSizeInBits(AddRec->getType());
@@ -4843,7 +4862,10 @@
if (CStep->isOne()) {
// With unit stride, the iteration never steps past the limit value.
} else if (CStep->getValue()->getValue().isStrictlyPositive()) {
- if (const SCEVConstant *CLimit = dyn_cast<SCEVConstant>(RHS)) {
+ if (NoWrap) {
+ // We know the iteration won't step past the maximum value for its type.
+ ;
+ } else if (const SCEVConstant *CLimit = dyn_cast<SCEVConstant>(RHS)) {
// Test whether a positive iteration iteration can step past the limit
// value and past the maximum value for its type in a single step.
if (isSigned) {
@@ -4896,11 +4918,11 @@
// Finally, we subtract these two values and divide, rounding up, to get
// the number of times the backedge is executed.
- const SCEV *BECount = getBECount(Start, End, Step);
+ const SCEV *BECount = getBECount(Start, End, Step, NoWrap);
// The maximum backedge count is similar, except using the minimum start
// value and the maximum end value.
- const SCEV *MaxBECount = getBECount(MinStart, MaxEnd, Step);
+ const SCEV *MaxBECount = getBECount(MinStart, MaxEnd, Step, NoWrap);
return BackedgeTakenInfo(BECount, MaxBECount);
}
Added: llvm/trunk/test/Analysis/ScalarEvolution/nsw-offset.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/nsw-offset.ll?rev=82151&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/nsw-offset.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/nsw-offset.ll Thu Sep 17 13:05:20 2009
@@ -0,0 +1,76 @@
+; RUN: opt < %s -S -analyze -scalar-evolution -disable-output | FileCheck %s
+
+; ScalarEvolution should be able to fold away the sign-extensions
+; on this loop with a primary induction variable incremented with
+; a nsw add of 2.
+
+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"
+
+define void @foo(i32 %n, double* nocapture %d, double* nocapture %q) nounwind {
+entry:
+ %0 = icmp sgt i32 %n, 0 ; <i1> [#uses=1]
+ br i1 %0, label %bb.nph, label %return
+
+bb.nph: ; preds = %entry
+ br label %bb
+
+bb: ; preds = %bb.nph, %bb1
+ %i.01 = phi i32 [ %16, %bb1 ], [ 0, %bb.nph ] ; <i32> [#uses=5]
+
+; CHECK: %1 = sext i32 %i.01 to i64
+; CHECK: --> {0,+,2}<bb>
+ %1 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
+
+; CHECK: %2 = getelementptr inbounds double* %d, i64 %1
+; CHECK: --> {%d,+,16}<bb>
+ %2 = getelementptr inbounds double* %d, i64 %1 ; <double*> [#uses=1]
+
+ %3 = load double* %2, align 8 ; <double> [#uses=1]
+ %4 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
+ %5 = getelementptr inbounds double* %q, i64 %4 ; <double*> [#uses=1]
+ %6 = load double* %5, align 8 ; <double> [#uses=1]
+ %7 = or i32 %i.01, 1 ; <i32> [#uses=1]
+
+; CHECK: %8 = sext i32 %7 to i64
+; CHECK: --> {1,+,2}<bb>
+ %8 = sext i32 %7 to i64 ; <i64> [#uses=1]
+
+; CHECK: %9 = getelementptr inbounds double* %q, i64 %8
+; CHECK: {(8 + %q),+,16}<bb>
+ %9 = getelementptr inbounds double* %q, i64 %8 ; <double*> [#uses=1]
+
+; Artificially repeat the above three instructions, this time using
+; add nsw instead of or.
+ %t7 = add nsw i32 %i.01, 1 ; <i32> [#uses=1]
+
+; CHECK: %t8 = sext i32 %t7 to i64
+; CHECK: --> {1,+,2}<bb>
+ %t8 = sext i32 %t7 to i64 ; <i64> [#uses=1]
+
+; CHECK: %t9 = getelementptr inbounds double* %q, i64 %t8
+; CHECK: {(8 + %q),+,16}<bb>
+ %t9 = getelementptr inbounds double* %q, i64 %t8 ; <double*> [#uses=1]
+
+ %10 = load double* %9, align 8 ; <double> [#uses=1]
+ %11 = fadd double %6, %10 ; <double> [#uses=1]
+ %12 = fadd double %11, 3.200000e+00 ; <double> [#uses=1]
+ %13 = fmul double %3, %12 ; <double> [#uses=1]
+ %14 = sext i32 %i.01 to i64 ; <i64> [#uses=1]
+ %15 = getelementptr inbounds double* %d, i64 %14 ; <double*> [#uses=1]
+ store double %13, double* %15, align 8
+ %16 = add nsw i32 %i.01, 2 ; <i32> [#uses=2]
+ br label %bb1
+
+bb1: ; preds = %bb
+ %17 = icmp slt i32 %16, %n ; <i1> [#uses=1]
+ br i1 %17, label %bb, label %bb1.return_crit_edge
+
+bb1.return_crit_edge: ; preds = %bb1
+ br label %return
+
+return: ; preds = %bb1.return_crit_edge, %entry
+ ret void
+}
+
+; CHECK: Loop bb: backedge-taken count is ((-1 + %n) /u 2)
+; CHECK: Loop bb: max backedge-taken count is 1073741823
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