diff options
| -rw-r--r-- | lib/Transforms/Scalar/IndVarSimplify.cpp | 30 | ||||
| -rw-r--r-- | test/Transforms/IndVarSimplify/lcssa-preservation.ll | 51 |
2 files changed, 74 insertions, 7 deletions
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp index 6f32549fdd..dfcd11fb4c 100644 --- a/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -497,6 +497,21 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { unsigned NumPreds = PN->getNumIncomingValues(); + // We would like to be able to RAUW single-incoming value PHI nodes. We + // have to be certain this is safe even when this is an LCSSA PHI node. + // While the computed exit value is no longer varying in *this* loop, the + // exit block may be an exit block for an outer containing loop as well, + // the exit value may be varying in the outer loop, and thus it may still + // require an LCSSA PHI node. The safe case is when this is + // single-predecessor PHI node (LCSSA) and the exit block containing it is + // part of the enclosing loop, or this is the outer most loop of the nest. + // In either case the exit value could (at most) be varying in the same + // loop body as the phi node itself. Thus if it is in turn used outside of + // an enclosing loop it will only be via a separate LCSSA node. + bool LCSSASafePhiForRAUW = + NumPreds == 1 && + (!L->getParentLoop() || L->getParentLoop() == LI->getLoopFor(ExitBB)); + // Iterate over all of the PHI nodes. BasicBlock::iterator BBI = ExitBB->begin(); while ((PN = dyn_cast<PHINode>(BBI++))) { @@ -597,17 +612,18 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { if (isInstructionTriviallyDead(Inst, TLI)) DeadInsts.push_back(Inst); - if (NumPreds == 1) { - // Completely replace a single-pred PHI. This is safe, because the - // NewVal won't be variant in the loop, so we don't need an LCSSA phi - // node anymore. + // If we determined that this PHI is safe to replace even if an LCSSA + // PHI, do so. + if (LCSSASafePhiForRAUW) { PN->replaceAllUsesWith(ExitVal); PN->eraseFromParent(); } } - if (NumPreds != 1) { - // Clone the PHI and delete the original one. This lets IVUsers and - // any other maps purge the original user from their records. + + // If we were unable to completely replace the PHI node, clone the PHI + // and delete the original one. This lets IVUsers and any other maps + // purge the original user from their records. + if (!LCSSASafePhiForRAUW) { PHINode *NewPN = cast<PHINode>(PN->clone()); NewPN->takeName(PN); NewPN->insertBefore(PN); diff --git a/test/Transforms/IndVarSimplify/lcssa-preservation.ll b/test/Transforms/IndVarSimplify/lcssa-preservation.ll new file mode 100644 index 0000000000..f69c96ce02 --- /dev/null +++ b/test/Transforms/IndVarSimplify/lcssa-preservation.ll @@ -0,0 +1,51 @@ +; RUN: opt < %s -indvars -S | FileCheck %s +; +; Make sure IndVars preserves LCSSA form, especially across loop nests. + +target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64" + +define void @PR18642(i32 %x) { +; CHECK-LABEL: @PR18642( +entry: + br label %outer.header +; CHECK: br label %outer.header + +outer.header: +; CHECK: outer.header: + %outer.iv = phi i32 [ 0, %entry ], [ %x, %outer.latch ] + br label %inner.header +; CHECK: %[[SCEV_EXPANDED:.*]] = add i32 +; CHECK: br label %inner.header + +inner.header: +; CHECK: inner.header: + %inner.iv = phi i32 [ undef, %outer.header ], [ %inc, %inner.latch ] + %cmp1 = icmp slt i32 %inner.iv, %outer.iv + br i1 %cmp1, label %inner.latch, label %outer.latch +; CHECK: br i1 {{.*}}, label %inner.latch, label %outer.latch + +inner.latch: +; CHECK: inner.latch: + %inc = add nsw i32 %inner.iv, 1 + %cmp2 = icmp slt i32 %inner.iv, %outer.iv + br i1 %cmp2, label %inner.header, label %exit +; CHECK: br i1 {{.*}}, label %inner.header, label %[[EXIT_FROM_INNER:.*]] + +outer.latch: +; CHECK: outer.latch: + br i1 undef, label %outer.header, label %exit +; CHECK: br i1 {{.*}}, label %outer.header, label %[[EXIT_FROM_OUTER:.*]] + +; CHECK: [[EXIT_FROM_INNER]]: +; CHECK-NEXT: %[[LCSSA:.*]] = phi i32 [ %[[SCEV_EXPANDED]], %inner.latch ] +; CHECK-NEXT: br label %exit + +; CHECK: [[EXIT_FROM_OUTER]]: +; CHECK-NEXT: br label %exit + +exit: +; CHECK: exit: + %exit.phi = phi i32 [ %inc, %inner.latch ], [ undef, %outer.latch ] +; CHECK-NEXT: phi i32 [ %[[LCSSA]], %[[EXIT_FROM_INNER]] ], [ undef, %[[EXIT_FROM_OUTER]] ] + ret void +} |