[llvm] 471217c - Revert "Revert "[IndVars] Replace PHIs if loop exits on 1st iteration""
Max Kazantsev via llvm-commits
llvm-commits at lists.llvm.org
Sun Sep 19 22:01:28 PDT 2021
Author: Max Kazantsev
Date: 2021-09-20T12:01:10+07:00
New Revision: 471217cff8e5c827f2ee52175a1c94584699cab2
URL: https://github.com/llvm/llvm-project/commit/471217cff8e5c827f2ee52175a1c94584699cab2
DIFF: https://github.com/llvm/llvm-project/commit/471217cff8e5c827f2ee52175a1c94584699cab2.diff
LOG: Revert "Revert "[IndVars] Replace PHIs if loop exits on 1st iteration""
This reverts commit 6fec6552f54885ae06bf76b35f9f1173a0561a4c.
The patch was reverted on incorrect claim that this patch may break LCSSA form
when the loop is not in a simplify form. All IndVars' transform insure that
the loop is in simplify and LCSSA form, so if it wasn't broken before this
transform, it will also not be broken after it.
Added:
Modified:
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll
llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 9b665bba4c97f..320e20ca341c5 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1309,6 +1309,17 @@ static void foldExit(const Loop *L, BasicBlock *ExitingBB, bool IsTaken,
replaceExitCond(BI, NewCond, DeadInsts);
}
+static void replaceLoopPHINodesWithPreheaderValues(
+ Loop *L, SmallVectorImpl<WeakTrackingVH> &DeadInsts) {
+ auto *LoopPreheader = L->getLoopPreheader();
+ auto *LoopHeader = L->getHeader();
+ for (auto &PN : LoopHeader->phis()) {
+ auto *PreheaderIncoming = PN.getIncomingValueForBlock(LoopPreheader);
+ PN.replaceAllUsesWith(PreheaderIncoming);
+ DeadInsts.emplace_back(&PN);
+ }
+}
+
static void replaceWithInvariantCond(
const Loop *L, BasicBlock *ExitingBB, ICmpInst::Predicate InvariantPred,
const SCEV *InvariantLHS, const SCEV *InvariantRHS, SCEVExpander &Rewriter,
@@ -1499,10 +1510,11 @@ bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) {
// If we know we'd exit on the first iteration, rewrite the exit to
// reflect this. This does not imply the loop must exit through this
// exit; there may be an earlier one taken on the first iteration.
- // TODO: Given we know the backedge can't be taken, we should go ahead
- // and break it. Or at least, kill all the header phis and simplify.
+ // We know that the backedge can't be taken, so we replace all
+ // the header PHIs with values coming from the preheader.
if (ExitCount->isZero()) {
foldExit(L, ExitingBB, true, DeadInsts);
+ replaceLoopPHINodesWithPreheaderValues(L, DeadInsts);
Changed = true;
continue;
}
diff --git a/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll b/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
index 34bc4f6384278..e2ba6e084dce6 100644
--- a/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
+++ b/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
@@ -15,16 +15,13 @@ define i1 @kill_backedge_and_phis(i8* align 1 %lhs, i8* align 1 %rhs, i32 %len)
; CHECK: loop_preheader:
; CHECK-NEXT: br label %loop
; CHECK: loop:
-; CHECK-NEXT: %iv = phi i32 [ 0, %loop_preheader ], [ %iv.next, %exiting_3 ]
-; CHECK-NEXT: %iv.wide = phi i64 [ 0, %loop_preheader ], [ %iv.wide.next, %exiting_3 ]
-; CHECK-NEXT: %iv.next = add nuw nsw i32 %iv, 1
-; CHECK-NEXT: %iv.wide.next = add nuw nsw i64 %iv.wide, 1
-; CHECK-NEXT: %left_ptr = getelementptr inbounds i8, i8* %lhs, i32 %iv
-; CHECK-NEXT: %right_ptr = getelementptr inbounds i8, i8* %rhs, i32 %iv
+; CHECK-NEXT: %iv.next = add nuw nsw i32 0, 1
+; CHECK-NEXT: %left_ptr = getelementptr inbounds i8, i8* %lhs, i32 0
+; CHECK-NEXT: %right_ptr = getelementptr inbounds i8, i8* %rhs, i32 0
; CHECK-NEXT: %result = call i1 @foo(i8* %left_ptr, i8* %right_ptr)
; CHECK-NEXT: br i1 %result, label %exiting_1, label %exit.loopexit
; CHECK: exiting_1:
-; CHECK-NEXT: %iv.wide.is_not_zero = icmp ne i64 %iv.wide, 0
+; CHECK-NEXT: %iv.wide.is_not_zero = icmp ne i64 0, 0
; CHECK-NEXT: br i1 false, label %exiting_2, label %exit.loopexit
; CHECK: exiting_2:
; CHECK-NEXT: %bar_ret = call i1 @bar()
diff --git a/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll b/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll
index 0abfb06bfe2b0..d8e0484b5207e 100644
--- a/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll
+++ b/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll
@@ -14,10 +14,9 @@ define void @foo() {
; CHECK-NEXT: bb:
; CHECK-NEXT: br label [[BB3:%.*]]
; CHECK: bb3:
-; CHECK-NEXT: [[TMP:%.*]] = phi i8* [ [[TMP4:%.*]], [[BB7:%.*]] ], [ getelementptr inbounds ([0 x i8], [0 x i8]* @global, i64 0, i64 2), [[BB:%.*]] ]
-; CHECK-NEXT: [[TMP4]] = getelementptr inbounds i8, i8* [[TMP]], i64 -1
+; CHECK-NEXT: [[TMP4:%.*]] = getelementptr inbounds i8, i8* getelementptr inbounds ([0 x i8], [0 x i8]* @global, i64 0, i64 2), i64 -1
; CHECK-NEXT: [[TMP6:%.*]] = load i8, i8* [[TMP4]], align 1
-; CHECK-NEXT: br i1 false, label [[BB7]], label [[BB11:%.*]]
+; CHECK-NEXT: br i1 false, label [[BB7:%.*]], label [[BB11:%.*]]
; CHECK: bb7:
; CHECK-NEXT: [[TMP8:%.*]] = zext i8 [[TMP6]] to i64
; CHECK-NEXT: br i1 true, label [[BB11]], label [[BB3]]
diff --git a/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll b/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll
index f22e606d929f6..ca081e81b3ee1 100644
--- a/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll
+++ b/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll
@@ -65,9 +65,7 @@ define void @test3() nounwind {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[BB:%.*]]
; CHECK: bb:
-; CHECK-NEXT: [[IV:%.*]] = phi double [ 0.000000e+00, [[ENTRY:%.*]] ], [ [[TMP1:%.*]], [[BB]] ]
-; CHECK-NEXT: [[TMP0:%.*]] = tail call i32 @foo(double [[IV]]) #[[ATTR0]]
-; CHECK-NEXT: [[TMP1]] = fadd double [[IV]], 1.000000e+00
+; CHECK-NEXT: [[TMP0:%.*]] = tail call i32 @foo(double 0.000000e+00) #[[ATTR0]]
; CHECK-NEXT: br i1 false, label [[BB]], label [[RETURN:%.*]]
; CHECK: return:
; CHECK-NEXT: ret void
More information about the llvm-commits
mailing list