[PATCH] D60935: [IndVarSimplify] Fixup nowrap flags during LFTR when moving to post-inc (PR31181)
Nikita Popov via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon May 20 14:08:55 PDT 2019
nikic updated this revision to Diff 200356.
nikic added a comment.
Handle pre-increment case as well, improve comment, rebase over additional tests.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D60935/new/
https://reviews.llvm.org/D60935
Files:
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
llvm/test/Transforms/IndVarSimplify/pr31181.ll
Index: llvm/test/Transforms/IndVarSimplify/pr31181.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/pr31181.ll
+++ llvm/test/Transforms/IndVarSimplify/pr31181.ll
@@ -15,7 +15,7 @@
; CHECK: loop:
; CHECK-NEXT: [[STOREMERGE:%.*]] = phi i32 [ -2, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[LOOP]] ]
; CHECK-NEXT: store i32 [[STOREMERGE]], i32* @a
-; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[STOREMERGE]], 1
+; CHECK-NEXT: [[INC]] = add nsw i32 [[STOREMERGE]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i32 [[INC]], 0
; CHECK-NEXT: br i1 [[EXITCOND]], label [[LOOP]], label [[EXIT:%.*]]
; CHECK: exit:
@@ -42,7 +42,7 @@
; CHECK: loop:
; CHECK-NEXT: [[STOREMERGE:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[LOOP]] ]
; CHECK-NEXT: store i32 [[STOREMERGE]], i32* @a
-; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[STOREMERGE]], 1
+; CHECK-NEXT: [[INC]] = add nuw i32 [[STOREMERGE]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i32 [[INC]], -2147483648
; CHECK-NEXT: br i1 [[EXITCOND]], label [[LOOP]], label [[EXIT:%.*]]
; CHECK: exit:
@@ -155,7 +155,7 @@
; CHECK: loop:
; CHECK-NEXT: [[STOREMERGE:%.*]] = phi i32 [ [[INC:%.*]], [[LOOP]] ], [ 0, [[LOOP_PREHEADER]] ]
; CHECK-NEXT: store i32 [[STOREMERGE]], i32* @a
-; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[STOREMERGE]], 1
+; CHECK-NEXT: [[INC]] = add nuw i32 [[STOREMERGE]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i32 [[INC]], [[TMP0]]
; CHECK-NEXT: br i1 [[EXITCOND]], label [[LOOP]], label [[EXIT_LOOPEXIT:%.*]]
; CHECK: exit.loopexit:
@@ -194,7 +194,7 @@
; CHECK-NEXT: br label [[ALWAYS_TAKEN]]
; CHECK: always_taken:
; CHECK-NEXT: [[IV_INC]] = add nsw i32 [[IV]], 1
-; CHECK-NEXT: [[IV2_INC]] = add nuw nsw i32 [[IV2]], 1
+; CHECK-NEXT: [[IV2_INC]] = add nuw i32 [[IV2]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i32 [[IV2_INC]], -2147483627
; CHECK-NEXT: br i1 [[EXITCOND]], label [[FOR_COND]], label [[FOR_END:%.*]]
; CHECK: for.end:
@@ -242,7 +242,7 @@
; CHECK-NEXT: br label [[ALWAYS_TAKEN]]
; CHECK: always_taken:
; CHECK-NEXT: [[IV_INC]] = add nsw i32 [[IV]], 1
-; CHECK-NEXT: [[IV2_INC]] = add nuw nsw i32 [[IV2]], 1
+; CHECK-NEXT: [[IV2_INC]] = add nuw i32 [[IV2]], 1
; CHECK-NEXT: br label [[FOR_COND]]
; CHECK: for.end:
; CHECK-NEXT: ret i32 0
Index: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -2372,6 +2372,27 @@
CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
}
+ // It may be necessary to drop nowrap flags on the incrementing instruction
+ // if either LFTR moves from a pre-inc check to a post-inc check (in which
+ // case the increment might have previously been poison on the last iteration
+ // only) or if LFTR switches to a different IV that was previously dynamically
+ // dead (and as such may be arbitrarily poison). We remove any nowrap flags
+ // that SCEV didn't infer for the post-inc addrec (even if we use a pre-inc
+ // check), because the pre-inc addrec flags may be adopted from the original
+ // instruction, while SCEV has to explicitly prove the post-inc nowrap flags.
+ // TODO: This handling may be inaccurate for one case: If we switch to a
+ // dynamically dead IV that wraps on the first loop iteration only, which is
+ // not covered by the post-inc addrec. (If the new IV was not dynamically
+ // dead, it could not be poison on the first iteration in the first place.)
+ Value *IncVar = IndVar->getIncomingValueForBlock(L->getLoopLatch());
+ if (auto *BO = dyn_cast<BinaryOperator>(IncVar)) {
+ const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(SE->getSCEV(IncVar));
+ if (BO->hasNoUnsignedWrap())
+ BO->setHasNoUnsignedWrap(AR->hasNoUnsignedWrap());
+ if (BO->hasNoSignedWrap())
+ BO->setHasNoSignedWrap(AR->hasNoSignedWrap());
+ }
+
Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE);
assert(ExitCnt->getType()->isPointerTy() ==
IndVar->getType()->isPointerTy() &&
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