[InstCombine] Widen guards with conditions between
The previous handling for guard widening in InstCombine was extremely restrictive. In particular, it didn't handle the common case where we had two guards separated by a single icmp. Handle this by scanning through a small fixed window of instructions to find the next guard if needed.
Differential Revision: https://reviews.llvm.org/D46203
llvm-svn: 331935
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c62b4d6..80b1957 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -79,6 +79,13 @@
cl::desc("Maximum number of elements in atomic memcpy the optimizer is "
"allowed to unfold"));
+static cl::opt<unsigned> GuardWideningWindow(
+ "instcombine-guard-widening-window",
+ cl::init(3),
+ cl::desc("How wide an instruction window to bypass looking for "
+ "another guard"));
+
+
/// Return the specified type promoted as it would be to pass though a va_arg
/// area.
static Type *getPromotedType(Type *Ty) {
@@ -3624,8 +3631,16 @@
}
case Intrinsic::experimental_guard: {
- // Is this guard followed by another guard?
+ // Is this guard followed by another guard? We scan forward over a small
+ // fixed window of instructions to handle common cases with conditions
+ // computed between guards.
Instruction *NextInst = II->getNextNode();
+ for (int i = 0; i < GuardWideningWindow; i++) {
+ // Note: Using context-free form to avoid compile time blow up
+ if (!isSafeToSpeculativelyExecute(NextInst))
+ break;
+ NextInst = NextInst->getNextNode();
+ }
Value *NextCond = nullptr;
if (match(NextInst,
m_Intrinsic<Intrinsic::experimental_guard>(m_Value(NextCond)))) {
@@ -3636,6 +3651,12 @@
return eraseInstFromFunction(*NextInst);
// Otherwise canonicalize guard(a); guard(b) -> guard(a & b).
+ Instruction* MoveI = II->getNextNode();
+ while (MoveI != NextInst) {
+ auto *Temp = MoveI;
+ MoveI = MoveI->getNextNode();
+ Temp->moveBefore(II);
+ }
II->setArgOperand(0, Builder.CreateAnd(CurrCond, NextCond));
return eraseInstFromFunction(*NextInst);
}