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Fix for two constant propagation problems in GVN with the assume intrinsic 

instruction.

Patch by Yuanrui Zhang.

Differential Revision: http://reviews.llvm.org/D16100

llvm-svn: 258435
This commit is contained in:
David L Kreitzer 2016-01-21 21:32:35 +00:00
parent 1f472eace5
commit 4d7257dfa1
4 changed files with 46 additions and 5 deletions
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2
llvm/include/llvm/Transforms/Utils/Local.h
View File

@ -316,7 +316,7 @@ void combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> Kn
unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT,
const BasicBlockEdge &Edge);
/// \brief Replace each use of 'From' with 'To' if that use is dominated by
/// the given BasicBlock. Returns the number of replacements made.
/// the end of the given BasicBlock. Returns the number of replacements made.
unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT,
const BasicBlock *BB);

7
llvm/lib/Transforms/Scalar/GVN.cpp
View File

@ -2133,7 +2133,8 @@ bool GVN::replaceOperandsWithConsts(Instruction *Instr) const {
/// The given values are known to be equal in every block
/// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with
/// 'RHS' everywhere in the scope. Returns whether a change was made.
/// If DominatesByEdge is false, then it means that it is dominated by Root.End.
/// If DominatesByEdge is false, then it means that we will propagate the RHS
/// value starting from the end of Root.Start.
bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
bool DominatesByEdge) {
SmallVector<std::pair<Value*, Value*>, 4> Worklist;
@ -2195,7 +2196,7 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
unsigned NumReplacements =
DominatesByEdge
? replaceDominatedUsesWith(LHS, RHS, *DT, Root)
: replaceDominatedUsesWith(LHS, RHS, *DT, Root.getEnd());
: replaceDominatedUsesWith(LHS, RHS, *DT, Root.getStart());
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
@ -2271,7 +2272,7 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
DominatesByEdge
? replaceDominatedUsesWith(NotCmp, NotVal, *DT, Root)
: replaceDominatedUsesWith(NotCmp, NotVal, *DT,
Root.getEnd());
Root.getStart());
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
}

2
llvm/lib/Transforms/Utils/Local.cpp
View File

@ -1569,7 +1569,7 @@ unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
UI != UE;) {
Use &U = *UI++;
auto *I = cast<Instruction>(U.getUser());
if (DT.dominates(BB, I->getParent())) {
if (DT.properlyDominates(BB, I->getParent())) {
U.set(To);
DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as "
<< *To << " in " << *U << "\n");

40
llvm/test/Transforms/GVN/assume-equal.ll
View File

@ -226,6 +226,46 @@ bb3:
ret i32 17
}
; This test checks if GVN can do the constant propagation correctly
; when there are multiple uses of the same assume value in the
; basic block that has a loop back-edge pointing to itself.
;
; CHECK-LABEL: define i32 @_Z1il(i32 %val, i1 %k)
define i32 @_Z1il(i32 %val, i1 %k) {
br label %next
next:
; CHECK: tail call void @llvm.assume(i1 %k)
; CHECK-NEXT: %cmp = icmp eq i32 %val, 50
tail call void @llvm.assume(i1 %k)
tail call void @llvm.assume(i1 %k)
%cmp = icmp eq i32 %val, 50
br i1 %cmp, label %next, label %meh
meh:
ret i32 0
}
; This test checks if GVN can prevent the constant propagation correctly
; in the successor blocks that are not dominated by the basic block
; with the assume instruction.
;
; CHECK-LABEL: define i1 @_z1im(i32 %val, i1 %k, i1 %j)
define i1 @_z1im(i32 %val, i1 %k, i1 %j) {
br i1 %j, label %next, label %meh
next:
; CHECK: tail call void @llvm.assume(i1 %k)
; CHECK-NEXT: br label %meh
tail call void @llvm.assume(i1 %k)
tail call void @llvm.assume(i1 %k)
br label %meh
meh:
; CHECK: ret i1 %k
ret i1 %k
}
declare noalias i8* @_Znwm(i64)
declare void @_ZN1AC1Ev(%struct.A*)
declare void @llvm.assume(i1)