Teach memdep to phi translate bitcasts. This allows us to compile
the example in GCC PR16799 to:
LBB1_2: ## %bb1
movl %eax, %eax
subq %rax, %rdi
movq %rdi, (%rcx)
movl (%rdi), %eax
testl %eax, %eax
je LBB1_2
instead of:
LBB1_2: ## %bb1
movl (%rdi), %ecx
subq %rcx, %rdi
movq %rdi, (%rax)
cmpl $0, (%rdi)
je LBB1_2
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89978 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index c4647b1..780d73e 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -690,10 +690,15 @@
if (isa<PHINode>(Inst))
return true;
- // TODO: BITCAST, GEP.
-
- // ...
+ // We can handle bitcast of a PHI, but the PHI needs to be in the same block
+ // as the bitcast.
+ if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst))
+ if (PHINode *PN = dyn_cast<PHINode>(BC->getOperand(0)))
+ if (PN->getParent() == BC->getParent())
+ return true;
+ // TODO: GEP, ...
+
// cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
// if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
// cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
@@ -708,6 +713,25 @@
if (PHINode *PN = dyn_cast<PHINode>(Inst))
return PN->getIncomingValueForBlock(Pred);
+ if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst)) {
+ PHINode *BCPN = cast<PHINode>(BC->getOperand(0));
+ Value *PHIIn = BCPN->getIncomingValueForBlock(Pred);
+
+ // Constants are trivial to phi translate.
+ if (Constant *C = dyn_cast<Constant>(PHIIn))
+ return ConstantExpr::getBitCast(C, BC->getType());
+
+ // Otherwise we have to see if a bitcasted version of the incoming pointer
+ // is available. If so, we can use it, otherwise we have to fail.
+ for (Value::use_iterator UI = PHIIn->use_begin(), E = PHIIn->use_end();
+ UI != E; ++UI) {
+ if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI))
+ if (BCI->getType() == BC->getType())
+ return BCI;
+ }
+ return 0;
+ }
+
return 0;
}