6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-06-21 18:24:23 +00:00
Code Issues Projects Releases Wiki Activity

Move previously dead code to handle computing the known bits of an alias

Browse Source 
up to where it actually works as intended. The problem is that
a GlobalAlias isa GlobalValue and so the prior block handled all of the
cases.

This allows us to constant fold based on the actual constant expression
in the global alias. As an example, see the last function in the newly
added test case which explicitly aligns an unaligned pointer using
constant expression math. Without this change, we fail to see that and
fold an alignment test to zero.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220164 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth
2014-10-19 09:06:56 +00:00
parent 0fd4e2e5a1
commit 4d2a706176
2 changed files with 51 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
lib/Analysis/ValueTracking.cpp
View File

@ -790,6 +790,17 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
return;
}
// A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
// the bits of its aliasee.
if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (GA->mayBeOverridden()) {
KnownZero.clearAllBits(); KnownOne.clearAllBits();
} else {
computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1, Q);
}
return;
}
// The address of an aligned GlobalValue has trailing zeros.
if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
unsigned Align = GV->getAlignment();
@ -815,16 +826,6 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
KnownOne.clearAllBits();
return;
}
// A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
// the bits of its aliasee.
if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (GA->mayBeOverridden()) {
KnownZero.clearAllBits(); KnownOne.clearAllBits();
} else {
computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1, Q);
}
return;
}
if (Argument *A = dyn_cast<Argument>(V)) {
unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0;