[llvm-commits] [llvm] r122712 - in /llvm/trunk: lib/Transforms/Scalar/LoopIdiomRecognize.cpp test/Transforms/LoopIdiom/basic.ll
Chris Lattner
sabre at nondot.org
Sun Jan 2 13:14:18 PST 2011
Author: lattner
Date: Sun Jan 2 15:14:18 2011
New Revision: 122712
URL: http://llvm.org/viewvc/llvm-project?rev=122712&view=rev
Log:
fix a miscompilation of tramp3d-v4: when forming a memcpy, we have to make
sure that the loop we're promoting into a memcpy doesn't mutate the input
of the memcpy. Before we were just checking that the dest of the memcpy
wasn't mod/ref'd by the loop.
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=122712&r1=122711&r2=122712&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp Sun Jan 2 15:14:18 2011
@@ -175,6 +175,10 @@
SmallVector<BasicBlock*, 8> ExitBlocks;
CurLoop->getUniqueExitBlocks(ExitBlocks);
+ DEBUG(dbgs() << "loop-idiom Scanning: F["
+ << L->getHeader()->getParent()->getName()
+ << "] Loop %" << L->getHeader()->getName() << "\n");
+
bool MadeChange = false;
// Scan all the blocks in the loop that are not in subloops.
for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
@@ -200,9 +204,6 @@
if (!DT->dominates(BB, ExitBlocks[i]))
return false;
- DEBUG(dbgs() << "loop-idiom Scanning: F[" << BB->getParent()->getName()
- << "] Loop %" << BB->getName() << "\n");
-
bool MadeChange = false;
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
// Look for store instructions, which may be memsets.
@@ -276,10 +277,11 @@
return false;
}
-/// mayLoopModRefLocation - Return true if the specified loop might do a load or
-/// store to the same location that the specified store could store to, which is
-/// a loop-strided access.
-static bool mayLoopModRefLocation(Value *Ptr, Loop *L, const SCEV *BECount,
+/// mayLoopAccessLocation - Return true if the specified loop might access the
+/// specified pointer location, which is a loop-strided access. The 'Access'
+/// argument specifies what the verboten forms of access are (read or write).
+static bool mayLoopAccessLocation(Value *Ptr,AliasAnalysis::ModRefResult Access,
+ Loop *L, const SCEV *BECount,
unsigned StoreSize, AliasAnalysis &AA,
StoreInst *IgnoredStore) {
// Get the location that may be stored across the loop. Since the access is
@@ -302,7 +304,7 @@
++BI)
for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
if (&*I != IgnoredStore &&
- AA.getModRefInfo(I, StoreLoc) != AliasAnalysis::NoModRef)
+ (AA.getModRefInfo(I, StoreLoc) & Access))
return true;
return false;
@@ -323,7 +325,8 @@
// 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 an alias.
- if (mayLoopModRefLocation(SI->getPointerOperand(), CurLoop, BECount,
+ if (mayLoopAccessLocation(SI->getPointerOperand(), AliasAnalysis::ModRef,
+ CurLoop, BECount,
StoreSize, getAnalysis<AliasAnalysis>(), SI))
return false;
@@ -386,10 +389,18 @@
// Okay, we have a strided store "p[i]" of a loaded value. We can turn
// this into a memcpy 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 (including the load feeding the stores).
+ // or write to the stored location (including the load feeding the stores).
// Check for an alias.
- if (mayLoopModRefLocation(SI->getPointerOperand(), CurLoop, BECount,
- StoreSize, getAnalysis<AliasAnalysis>(), SI))
+ if (mayLoopAccessLocation(SI->getPointerOperand(), AliasAnalysis::ModRef,
+ CurLoop, BECount, StoreSize,
+ getAnalysis<AliasAnalysis>(), SI))
+ return false;
+
+ // For a memcpy, we have to make sure that the input array is not being
+ // mutated by the loop.
+ if (mayLoopAccessLocation(LI->getPointerOperand(), AliasAnalysis::Mod,
+ CurLoop, BECount, StoreSize,
+ getAnalysis<AliasAnalysis>(), SI))
return false;
// Okay, everything looks good, insert the memcpy.
Modified: llvm/trunk/test/Transforms/LoopIdiom/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopIdiom/basic.ll?rev=122712&r1=122711&r2=122712&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopIdiom/basic.ll (original)
+++ llvm/trunk/test/Transforms/LoopIdiom/basic.ll Sun Jan 2 15:14:18 2011
@@ -207,3 +207,36 @@
; CHECK: store i64 0, i64* %PI
}
+declare i8* @external(i8*)
+
+;; This cannot be transformed into a memcpy, because the read-from location is
+;; mutated by the loop.
+define void @test9(i64 %Size) nounwind ssp {
+bb.nph:
+ %Base = alloca i8, i32 10000
+ %Dest = alloca i8, i32 10000
+
+ %BaseAlias = call i8* @external(i8* %Base)
+ br label %for.body
+
+for.body: ; preds = %bb.nph, %for.body
+ %indvar = phi i64 [ 0, %bb.nph ], [ %indvar.next, %for.body ]
+ %I.0.014 = getelementptr i8* %Base, i64 %indvar
+ %DestI = getelementptr i8* %Dest, i64 %indvar
+ %V = load i8* %I.0.014, align 1
+ store i8 %V, i8* %DestI, align 1
+
+ ;; This store can clobber the input.
+ store i8 4, i8* %BaseAlias
+
+ %indvar.next = add i64 %indvar, 1
+ %exitcond = icmp eq i64 %indvar.next, %Size
+ br i1 %exitcond, label %for.end, label %for.body
+
+for.end: ; preds = %for.body, %entry
+ ret void
+; CHECK: @test9
+; CHECK-NOT: llvm.memcpy
+; CHECK: ret void
+}
+
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