RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-23 03:02:36 +01:00
Code Issues Projects Releases Wiki Activity

[IndVars] Fix PR25576

Browse Source 
`LCSSASafePhiForRAUW` as computed was incorrect -- in cases like
these (this exact example does not actually trigger the bug):

define i32 @f(i32 %n, i1* %c) {
entry:
  br label %outer.loop

outer.loop:
  br label %inner.loop

inner.loop:
  %iv = phi i32 [ 0, %outer.loop ], [ %iv.inc, %inner.loop ]
  %iv.inc = add nuw nsw i32 %iv, 1
  %tc = udiv i32 %n, 13
  %be.cond = icmp ult i32 %iv, %tc
  br i1 %be.cond, label %inner.loop, label %inner.exit

inner.exit:
  %iv.lcssa = phi i32 [ %iv, %inner.loop ]
  %outer.be.cond = load volatile i1, i1* %c
  br i1 %outer.be.cond, label %outer.loop, label %leave

leave:
  %iv.lcssa.lcssa = phi i32 [ %iv.lcssa, %inner.exit ]
  ret i32 %iv.lcssa.lcssa
}

`LCSSASafePhiForRAUW` is true for `%iv.lcssa` when re-rewriting the exit
value of `%iv` for `%inner.loop` to `%tc` (this can happen due to
`SCEVExpander::findExistingExpansion`), but the RAUW breaks LCSSA.

To fix this, instead of computing `SafePhi` with special logic, decide
the safety of RAUW directly via `replacementPreservesLCSSAForm`.

llvm-svn: 258016
This commit is contained in:
Sanjoy Das 2016-01-17 18:12:52 +00:00
parent 2c8efc2a82
commit aa011535f3
2 changed files with 37 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -504,10 +504,9 @@ struct RewritePhi {
unsigned Ith; // Ith incoming value.
Value *Val; // Exit value after expansion.
bool HighCost; // High Cost when expansion.
bool SafePhi; // LCSSASafePhiForRAUW.
RewritePhi(PHINode *P, unsigned I, Value *V, bool H, bool S)
: PN(P), Ith(I), Val(V), HighCost(H), SafePhi(S) {}
RewritePhi(PHINode *P, unsigned I, Value *V, bool H)
: PN(P), Ith(I), Val(V), HighCost(H) {}
};
}
@ -560,21 +559,6 @@ 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++))) {
@ -669,8 +653,7 @@ void IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
}
// Collect all the candidate PHINodes to be rewritten.
RewritePhiSet.emplace_back(PN, i, ExitVal, HighCost,
LCSSASafePhiForRAUW);
RewritePhiSet.emplace_back(PN, i, ExitVal, HighCost);
}
}
}
@ -699,9 +682,9 @@ void IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
if (isInstructionTriviallyDead(Inst, TLI))
DeadInsts.push_back(Inst);
// If we determined that this PHI is safe to replace even if an LCSSA
// PHI, do so.
if (Phi.SafePhi) {
// Replace PN with ExitVal if that is legal and does not break LCSSA.
if (PN->getNumIncomingValues() == 1 &&
LI->replacementPreservesLCSSAForm(PN, ExitVal)) {
PN->replaceAllUsesWith(ExitVal);
PN->eraseFromParent();
}

31
test/Transforms/IndVarSimplify/pr25576.ll Normal file
View File

@ -0,0 +1,31 @@
; RUN: opt -S -indvars < %s | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define void @fn1() {
; CHECK-LABEL: @fn1(
entry:
br label %for.cond.loopexit
for.cond.loopexit: ; preds = %for.inc7, %for.cond.loopexit, %entry
%c.1.lcssa = phi i32 [ %inc8, %for.inc7 ], [ 0, %for.cond.loopexit ], [ 0, %entry ]
br i1 undef, label %for.cond.loopexit, label %for.cond4.preheader
for.cond4.preheader: ; preds = %for.inc7, %for.cond.loopexit
%c.17 = phi i32 [ %inc8, %for.inc7 ], [ 0, %for.cond.loopexit ]
br label %for.body6
for.body6: ; preds = %for.body6, %for.cond4.preheader
%inc14 = phi i32 [ 0, %for.cond4.preheader ], [ %inc, %for.body6 ]
%idxprom = zext i32 %inc14 to i64
%inc = add i32 %inc14, 1
%cmp5 = icmp ult i32 %inc, 2
br i1 %cmp5, label %for.body6, label %for.inc7
for.inc7: ; preds = %for.body6
%inc.lcssa = phi i32 [ %inc, %for.body6 ]
%inc8 = add i32 %c.17, 1
%cmp = icmp ult i32 %inc8, %inc.lcssa
br i1 %cmp, label %for.cond4.preheader, label %for.cond.loopexit
}