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[BDCE] Don't forget uses of root instructions seen before the instruction itself

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When visiting the initial list of "root" instructions (those which must always
be alive), for those that are integer-valued (such as invokes returning an
integer), we mark their bits as (initially) all dead (we might, obviously, find
uses of those bits later, but all bits are assumed dead until proven
otherwise). Don't do so, however, if we're already seen a use of those bits by
another root instruction (such as a store).

Fixes a miscompile of the sanitizer unit tests on x86_64.

Also, add a debug line for visiting the root instructions, and remove a debug
line which tried to print instructions being removed (printing dead
instructions is dangerous, and can sometimes crash).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229618 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel 2015-02-18 03:12:28 +00:00
parent 333507b7af
commit 8a85dee989
2 changed files with 43 additions and 3 deletions
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9
lib/Transforms/Scalar/BDCE.cpp
View File

@ -277,13 +277,17 @@ bool BDCE::runOnFunction(Function& F) {
if (!isAlwaysLive(&I))
continue;
DEBUG(dbgs() << "BDCE: Root: " << I);
// For integer-valued instructions, set up an initial empty set of alive
// bits and add the instruction to the work list. For other instructions
// add their operands to the work list (for integer values operands, mark
// all bits as live).
if (IntegerType *IT = dyn_cast<IntegerType>(I.getType())) {
AliveBits[&I] = APInt(IT->getBitWidth(), 0);
Worklist.push_back(&I);
if (!AliveBits.count(&I)) {
AliveBits[&I] = APInt(IT->getBitWidth(), 0);
Worklist.push_back(&I);
}
continue;
}
@ -388,7 +392,6 @@ bool BDCE::runOnFunction(Function& F) {
if (isAlwaysLive(&I))
continue;
DEBUG(dbgs() << "BDCE: Removing: " << I << " (unused)\n");
Worklist.push_back(&I);
I.dropAllReferences();
Changed = true;

37
test/Transforms/BDCE/order.ll Normal file
View File

@ -0,0 +1,37 @@
; RUN: opt -bdce -S < %s | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
declare i32 @__gxx_personality_v0(...)
define fastcc void @_ZN11__sanitizerL12TestRegistryEPNS_14ThreadRegistryEb() #0 {
entry:
br i1 undef, label %if.else, label %entry.if.end_crit_edge
if.else:
ret void
invoke.cont70:
store i32 %call71, i32* undef, align 4
br label %if.else
; CHECK-LABEL: @_ZN11__sanitizerL12TestRegistryEPNS_14ThreadRegistryEb
; CHECK: store i32 %call71
lpad65.loopexit.split-lp.loopexit.split-lp:
br label %if.else
lpad65.loopexit.split-lp.loopexit.split-lp.loopexit:
%lpad.loopexit1121 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*)
cleanup
br label %lpad65.loopexit.split-lp.loopexit.split-lp
entry.if.end_crit_edge:
%call71 = invoke i32 @_ZN11__sanitizer14ThreadRegistry12CreateThreadEmbjPv()
to label %invoke.cont70 unwind label %lpad65.loopexit.split-lp.loopexit.split-lp.loopexit
}
declare i32 @_ZN11__sanitizer14ThreadRegistry12CreateThreadEmbjPv()
attributes #0 = { uwtable }