const SCEV *BackedgeTakenCount = getBackedgeTakenCount(LI);
if (const SCEVConstant *BTCC =
dyn_cast<SCEVConstant>(BackedgeTakenCount)) {
+
+ // This trivial case can show up in some degenerate cases where
+ // the incoming IR has not yet been fully simplified.
+ if (BTCC->getValue()->isZero()) {
+ Value *InitValue = nullptr;
+ bool MultipleInitValues = false;
+ for (unsigned i = 0; i < PN->getNumIncomingValues(); i++) {
+ if (!LI->contains(PN->getIncomingBlock(i))) {
+ if (!InitValue)
+ InitValue = PN->getIncomingValue(i);
+ else if (InitValue != PN->getIncomingValue(i)) {
+ MultipleInitValues = true;
+ break;
+ }
+ }
+ if (!MultipleInitValues && InitValue)
+ return getSCEV(InitValue);
+ }
+ }
// Okay, we know how many times the containing loop executes. If
// this is a constant evolving PHI node, get the final value at
// the specified iteration number.
; Check IndVarSimplify should not replace exit value because or else
; udiv will be introduced by expand and the cost will be high.
-;
-; CHECK-LABEL: @_Z3fooPKcjj(
-; CHECK-NOT: udiv
declare void @_Z3mixRjj(i32* dereferenceable(4), i32)
declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)
define i32 @_Z3fooPKcjj(i8* nocapture readonly %s, i32 %len, i32 %c) {
+; CHECK-LABEL: @_Z3fooPKcjj(
+; CHECK-NOT: udiv
entry:
%a = alloca i32, align 4
%tmp = bitcast i32* %a to i8*
call void @llvm.lifetime.end.p0i8(i64 4, i8* %tmp)
ret i32 %tmp4
}
+
+define i32 @zero_backedge_count_test(i32 %unknown_init, i32* %unknown_mem) {
+; CHECK-LABEL: @zero_backedge_count_test(
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry], [ %iv.inc, %loop ]
+ %unknown_phi = phi i32 [ %unknown_init, %entry ], [ %unknown_next, %loop ]
+ %iv.inc = add i32 %iv, 1
+ %be_taken = icmp ne i32 %iv.inc, 1
+ %unknown_next = load volatile i32, i32* %unknown_mem
+ br i1 %be_taken, label %loop, label %leave
+
+leave:
+; We can fold %unknown_phi even though the backedge value for it is completely
+; unknown, since we can prove that the loop's backedge taken count is 0.
+
+; CHECK: leave:
+; CHECK: ret i32 %unknown_init
+ %exit_val = phi i32 [ %unknown_phi, %loop ]
+ ret i32 %exit_val
+}