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ValueTracking: ComputeNumSignBits should tolerate misshapen phi nodes 

PHI nodes can have zero operands in the middle of a transform.  It is
expected that utilities in Analysis don't freak out when this happens.

Note that it is considered invalid to allow these misshapen phi nodes to
make it to another pass.

This fixes PR22086.

llvm-svn: 225126
This commit is contained in:
David Majnemer 2015-01-04 07:06:53 +00:00
parent 227822e116
commit 6ee8d17bc6
2 changed files with 33 additions and 2 deletions
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7
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -1821,13 +1821,16 @@ unsigned ComputeNumSignBits(Value *V, const DataLayout *TD,
case Instruction::PHI: {
PHINode *PN = cast<PHINode>(U);
unsigned NumIncomingValues = PN->getNumIncomingValues();
// Don't analyze large in-degree PHIs.
if (PN->getNumIncomingValues() > 4) break;
if (NumIncomingValues > 4) break;
// Unreachable blocks may have zero-operand PHI nodes.
if (NumIncomingValues == 0) break;
// Take the minimum of all incoming values. This can't infinitely loop
// because of our depth threshold.
Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1, Q);
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
if (Tmp == 1) return Tmp;
Tmp = std::min(Tmp,
ComputeNumSignBits(PN->getIncomingValue(i), TD,

28
llvm/test/Transforms/JumpThreading/pr22086.ll Normal file
View File

@ -0,0 +1,28 @@
; RUN: opt -S -jump-threading < %s | FileCheck %s
; CHECK-LABEL: @f(
; CHECK-LABEL: entry:
; CHECK-NEXT: br label %[[loop:.*]]
; CHECK: [[loop]]:
; CHECK-NEXT: br label %[[loop]]
define void @f() {
entry:
br label %for.cond1
if.end16:
%phi1 = phi i32 [ undef, %for.cond1 ]
%g.3 = phi i32 [ %g.1, %for.cond1 ]
%sext = shl i32 %g.3, 16
%conv20 = ashr exact i32 %sext, 16
%tobool21 = icmp eq i32 %phi1, 0
br i1 %tobool21, label %lor.rhs, label %for.cond1
for.cond1:
%g.1 = phi i32 [ 0, %entry ], [ 0, %lor.rhs ], [ %g.3, %if.end16 ]
br i1 undef, label %lor.rhs, label %if.end16
lor.rhs:
br label %for.cond1
}