[llvm] r251512 - [LIR] Add support for creating memsets from loops with a negative stride.
Chad Rosier via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 28 05:55:35 PDT 2015
Author: mcrosier
Date: Wed Oct 28 07:55:34 2015
New Revision: 251512
URL: http://llvm.org/viewvc/llvm-project?rev=251512&view=rev
Log:
[LIR] Add support for creating memsets from loops with a negative stride.
http://reviews.llvm.org/D14125
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
llvm/trunk/test/Transforms/LoopIdiom/basic.ll
Modified: llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp?rev=251512&r1=251511&r2=251512&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp Wed Oct 28 07:55:34 2015
@@ -31,11 +31,6 @@
// void foo(_Complex float *P)
// for (i) { __real__(*P) = 0; __imag__(*P) = 0; }
//
-// We should enhance this to handle negative strides through memory.
-// Alternatively (and perhaps better) we could rely on an earlier pass to force
-// forward iteration through memory, which is generally better for cache
-// behavior. Negative strides *do* happen for memset/memcpy loops.
-//
// This could recognize common matrix multiplies and dot product idioms and
// replace them with calls to BLAS (if linked in??).
//
@@ -124,7 +119,7 @@ private:
bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
unsigned StoreAlignment, Value *SplatValue,
Instruction *TheStore, const SCEVAddRecExpr *Ev,
- const SCEV *BECount);
+ const SCEV *BECount, bool NegStride);
bool processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
const SCEVAddRecExpr *StoreEv,
const SCEVAddRecExpr *LoadEv,
@@ -316,23 +311,21 @@ bool LoopIdiomRecognize::processLoopStor
// Check to see if the stride matches the size of the store. If so, then we
// know that every byte is touched in the loop.
unsigned StoreSize = (unsigned)SizeInBits >> 3;
- const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
- if (!Stride || StoreSize != Stride->getValue()->getValue()) {
- // TODO: Could also handle negative stride here someday, that will require
- // the validity check in mayLoopAccessLocation to be updated though.
- // Enable this to print exact negative strides.
- if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
- dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
- dbgs() << "BB: " << *SI->getParent();
- }
+ const SCEVConstant *ConstStride =
+ dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
+ if (!ConstStride)
+ return false;
+ APInt Stride = ConstStride->getValue()->getValue();
+ if (StoreSize != Stride && StoreSize != -Stride)
return false;
- }
+
+ bool NegStride = StoreSize == -Stride;
// See if we can optimize just this store in isolation.
if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
- StoredVal, SI, StoreEv, BECount))
+ StoredVal, SI, StoreEv, BECount, NegStride))
return true;
// If the stored value is a strided load in the same loop with the same stride
@@ -387,7 +380,7 @@ bool LoopIdiomRecognize::processLoopMemS
return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
MSI->getAlignment(), MSI->getValue(), MSI, Ev,
- BECount);
+ BECount, /*NegStride=*/false);
}
/// mayLoopAccessLocation - Return true if the specified loop might access the
@@ -468,7 +461,7 @@ static Constant *getMemSetPatternValue(V
bool LoopIdiomRecognize::processLoopStridedStore(
Value *DestPtr, unsigned StoreSize, unsigned StoreAlignment,
Value *StoredVal, Instruction *TheStore, const SCEVAddRecExpr *Ev,
- const SCEV *BECount) {
+ const SCEV *BECount, bool NegStride) {
// If the stored value is a byte-wise value (like i32 -1), then it may be
// turned into a memset of i8 -1, assuming that all the consecutive bytes
@@ -506,15 +499,27 @@ bool LoopIdiomRecognize::processLoopStri
SCEVExpander Expander(*SE, DL, "loop-idiom");
Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
+ Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
+
+ const SCEV *Start = Ev->getStart();
+ // If we have a negative stride, Start refers to the end of the memory
+ // location we're trying to memset. Therefore, we need to recompute the start
+ // point, which is just Start - BECount*Size.
+ if (NegStride) {
+ const SCEV *Index = SE->getTruncateOrZeroExtend(BECount, IntPtr);
+ if (StoreSize != 1)
+ Index = SE->getMulExpr(Index, SE->getConstant(IntPtr, StoreSize),
+ SCEV::FlagNUW);
+ Start = SE->getMinusSCEV(Ev->getStart(), Index);
+ }
// Okay, we have a strided store "p[i]" of a splattable value. We can turn
// this into a memset in the loop preheader now if we want. However, this
// would be unsafe to do if there is anything else in the loop that may read
// or write to the aliased location. Check for any overlap by generating the
// base pointer and checking the region.
- Value *BasePtr = Expander.expandCodeFor(Ev->getStart(), DestInt8PtrTy,
- Preheader->getTerminator());
-
+ Value *BasePtr =
+ Expander.expandCodeFor(Start, DestInt8PtrTy, Preheader->getTerminator());
if (mayLoopAccessLocation(BasePtr, MRI_ModRef, CurLoop, BECount, StoreSize,
*AA, TheStore)) {
Expander.clear();
@@ -527,7 +532,6 @@ bool LoopIdiomRecognize::processLoopStri
// The # stored bytes is (BECount+1)*Size. Expand the trip count out to
// pointer size if it isn't already.
- Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);
const SCEV *NumBytesS =
Modified: llvm/trunk/test/Transforms/LoopIdiom/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopIdiom/basic.ll?rev=251512&r1=251511&r2=251512&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopIdiom/basic.ll (original)
+++ llvm/trunk/test/Transforms/LoopIdiom/basic.ll Wed Oct 28 07:55:34 2015
@@ -424,3 +424,47 @@ exit:
ret void
; CHECK: ret void
}
+
+; Recognize loops with a negative stride.
+define void @test15(i32* nocapture %f) {
+entry:
+ br label %for.body
+
+for.body:
+ %indvars.iv = phi i64 [ 65536, %entry ], [ %indvars.iv.next, %for.body ]
+ %arrayidx = getelementptr inbounds i32, i32* %f, i64 %indvars.iv
+ store i32 0, i32* %arrayidx, align 4
+ %indvars.iv.next = add nsw i64 %indvars.iv, -1
+ %cmp = icmp sgt i64 %indvars.iv, 0
+ br i1 %cmp, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup:
+ ret void
+; CHECK-LABEL: @test15(
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %f1, i8 0, i64 262148, i32 4, i1 false)
+; CHECK-NOT: store
+; CHECK: ret void
+}
+
+; Loop with a negative stride. Verify an aliasing write to f[65536] prevents
+; the creation of a memset.
+define void @test16(i32* nocapture %f) {
+entry:
+ %arrayidx1 = getelementptr inbounds i32, i32* %f, i64 65536
+ br label %for.body
+
+for.body: ; preds = %entry, %for.body
+ %indvars.iv = phi i64 [ 65536, %entry ], [ %indvars.iv.next, %for.body ]
+ %arrayidx = getelementptr inbounds i32, i32* %f, i64 %indvars.iv
+ store i32 0, i32* %arrayidx, align 4
+ store i32 1, i32* %arrayidx1, align 4
+ %indvars.iv.next = add nsw i64 %indvars.iv, -1
+ %cmp = icmp sgt i64 %indvars.iv, 0
+ br i1 %cmp, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup: ; preds = %for.body
+ ret void
+; CHECK-LABEL: @test16(
+; CHECK-NOT: call void @llvm.memset.p0i8.i64
+; CHECK: ret void
+}
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