const SCEVAddRecExpr *PreAR = dyn_cast<SCEVAddRecExpr>(
SE->getAddRecExpr(PreStart, Step, L, SCEV::FlagAnyWrap));
- // WARNING: FIXME: the optimization below assumes that a sign/zero-overflowing
- // nsw/nuw operation is undefined behavior. This is strictly more aggressive
- // than the interpretation of nsw in other parts of LLVM (for instance, they
- // may unconditionally hoist nsw/nuw arithmetic through control flow). This
- // logic needs to be revisited once we have a consistent semantics for poison
- // values.
- //
- // "{S,+,X} is <nsw>/<nuw>" and "{S,+,X} is evaluated at least once" implies
- // "S+X does not sign/unsign-overflow" (we'd have undefined behavior if it
- // did). If `L->getExitingBlock() == L->getLoopLatch()` then `PreAR` (=
- // {S,+,X}<nsw>/<nuw>) is evaluated every-time `AR` (= {S+X,+,X}) is
- // evaluated, and hence within `AR` we are safe to assume that "S+X" will not
- // sign/unsign-overflow.
+ // "{S,+,X} is <nsw>/<nuw>" and "the backedge is taken at least once" implies
+ // "S+X does not sign/unsign-overflow".
//
- BasicBlock *ExitingBlock = L->getExitingBlock();
- BasicBlock *LatchBlock = L->getLoopLatch();
- if (PreAR && PreAR->getNoWrapFlags(WrapType) && ExitingBlock != nullptr &&
- ExitingBlock == LatchBlock)
+ const SCEV *BECount = SE->getBackedgeTakenCount(L);
+ if (PreAR && PreAR->getNoWrapFlags(WrapType) &&
+ !isa<SCEVCouldNotCompute>(BECount) && SE->isKnownPositive(BECount))
return PreStart;
// 2. Direct overflow check on the step operation's expression.
br label %loop
loop:
+ %counter = phi i32 [ 0, %entry ], [ %counter.inc, %loop ]
%idx = phi i32 [ %start, %entry ], [ %idx.inc, %loop ]
%idx.inc = add nsw i32 %idx, 1
%idx.inc.sext = sext i32 %idx.inc to i64
; CHECK: %idx.inc.sext = sext i32 %idx.inc to i64
; CHECK-NEXT: --> {(1 + (sext i32 %start to i64)),+,1}<nsw><%loop>
- %condition = load volatile i1* %c
+ %condition = icmp eq i32 %counter, 1
+ %counter.inc = add i32 %counter, 1
br i1 %condition, label %exit, label %loop
exit:
br label %loop
loop:
+ %counter = phi i32 [ 0, %entry ], [ %counter.inc, %loop ]
%idx = phi i32 [ %start, %entry ], [ %idx.inc, %loop ]
%idx.inc = add nuw i32 %idx, 1
%idx.inc.sext = zext i32 %idx.inc to i64
; CHECK: %idx.inc.sext = zext i32 %idx.inc to i64
; CHECK-NEXT: --> {(1 + (zext i32 %start to i64)),+,1}<nuw><%loop>
- %condition = load volatile i1* %c
+ %condition = icmp eq i32 %counter, 1
+ %counter.inc = add i32 %counter, 1
br i1 %condition, label %exit, label %loop
exit:
--- /dev/null
+; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
+
+define i1 @main(i16 %a) {
+; CHECK-LABEL: Classifying expressions for: @main
+entry:
+ br label %body
+
+body:
+ %dec2 = phi i16 [ %a, %entry ], [ %dec, %cond ]
+ %dec = add i16 %dec2, -1
+ %conv2 = zext i16 %dec2 to i32
+ %conv = zext i16 %dec to i32
+; CHECK: %conv = zext i16 %dec to i32
+; CHECK-NEXT: --> {(zext i16 (-1 + %a) to i32),+,65535}<nuw><%body>
+; CHECK-NOT: --> {(65535 + (zext i16 %a to i32)),+,65535}<nuw><%body>
+
+ br label %cond
+
+cond:
+ br i1 false, label %body, label %exit
+
+exit:
+ %ret = icmp ne i32 %conv, 0
+ ret i1 %ret
+}
early.exit:
ret i64 %postinc.sext
}
-
-
-; WARNING: FIXME: it is safe to make the inference demonstrated here
-; only if we assume `add nsw` has undefined behavior if the result
-; sign-overflows; and this interpretation is stronger than what most
-; of LLVM assumes. This test here only serves as a documentation of
-; current behavior and will need to be revisited once we've decided
-; upon a consistent semantics for nsw (and nuw) arithetic operations.
-;
-define i64 @good(i32 %start, i32 %low.limit, i32 %high.limit) {
-; CHECK-LABEL: Classifying expressions for: @good
- entry:
- %postinc.start = add i32 %start, 1
- br label %loop
-
- loop:
- %idx = phi i32 [ %start, %entry ], [ %idx.inc, %loop ]
- %postinc = phi i32 [ %postinc.start, %entry ], [ %postinc.inc, %loop ]
- %postinc.inc = add nsw i32 %postinc, 1
- %postinc.sext = sext i32 %postinc to i64
-; CHECK: %postinc.sext = sext i32 %postinc to i64
-; CHECK-NEXT: --> {(1 + (sext i32 %start to i64)),+,1}<nsw><%loop>
-
- %break.early = icmp slt i32 %postinc, %low.limit
- %idx.inc = add nsw i32 %idx, 1
- %cmp = icmp slt i32 %idx.inc, %high.limit
- br i1 %cmp, label %loop, label %exit
-
- exit:
- ret i64 0
-
- early.exit:
- ret i64 %postinc.sext
-}