fix PR8642: if a critical edge has a PHI value that can trap,
isel is *required* to split the edge. PHI values get evaluated
on the edge, not in their predecessor block.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122170 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 5095646..42fd78f 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -43,6 +43,7 @@
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
@@ -239,6 +240,44 @@
#undef NUM_RETURNS_TWICE_FNS
}
+/// SplitCriticalSideEffectEdges - Look for critical edges with a PHI value that
+/// may trap on it. In this case we have to split the edge so that the path
+/// through the predecessor block that doesn't go to the phi block doesn't
+/// execute the possibly trapping instruction.
+///
+/// This is required for correctness, so it must be done at -O0.
+///
+static void SplitCriticalSideEffectEdges(Function &Fn, Pass *SDISel) {
+ // Loop for blocks with phi nodes.
+ for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
+ PHINode *PN = dyn_cast<PHINode>(BB->begin());
+ if (PN == 0) continue;
+
+ ReprocessBlock:
+ // For each block with a PHI node, check to see if any of the input values
+ // are potentially trapping constant expressions. Constant expressions are
+ // the only potentially trapping value that can occur as the argument to a
+ // PHI.
+ for (BasicBlock::iterator I = BB->begin(); (PN = dyn_cast<PHINode>(I)); ++I)
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ ConstantExpr *CE = dyn_cast<ConstantExpr>(PN->getIncomingValue(i));
+ if (CE == 0 || !CE->canTrap()) continue;
+
+ // The only case we have to worry about is when the edge is critical.
+ // Since this block has a PHI Node, we assume it has multiple input
+ // edges: check to see if the pred has multiple successors.
+ BasicBlock *Pred = PN->getIncomingBlock(i);
+ if (Pred->getTerminator()->getNumSuccessors() == 1)
+ continue;
+
+ // Okay, we have to split this edge.
+ SplitCriticalEdge(Pred->getTerminator(),
+ GetSuccessorNumber(Pred, BB), SDISel, true);
+ goto ReprocessBlock;
+ }
+ }
+}
+
bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
// Do some sanity-checking on the command-line options.
assert((!EnableFastISelVerbose || EnableFastISel) &&
@@ -257,6 +296,8 @@
DEBUG(dbgs() << "\n\n\n=== " << Fn.getName() << "\n");
+ SplitCriticalSideEffectEdges(const_cast<Function&>(Fn), this);
+
CurDAG->init(*MF);
FuncInfo->set(Fn, *MF);
SDB->init(GFI, *AA);