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[IR] allow fast-math-flags on phi of FP values

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The changes here are based on the corresponding diffs for allowing FMF on 'select':
D61917

As discussed there, we want to have fast-math-flags be a property of an FP value
because the alternative (having them on things like fcmp) leads to logical
inconsistency such as:
https://bugs.llvm.org/show_bug.cgi?id=38086

The earlier patch for select made almost no practical difference because most
unoptimized conditional code begins life as a phi (based on what I see in clang).
Similarly, I don't expect this patch to do much on its own either because
SimplifyCFG promptly drops the flags when converting to select on a minimal
example like:
https://bugs.llvm.org/show_bug.cgi?id=39535

But once we have this plumbing in place, we should be able to wire up the FMF
propagation and start solving cases like that.

The change to RecurrenceDescriptor::AddReductionVar() is required to prevent a
regression in a LoopVectorize test. We are intersecting the FMF of any
FPMathOperator there, so if a phi is not properly annotated, new math
instructions may not be either. Once we fix the propagation in SimplifyCFG, it
may be safe to remove that hack.

Differential Revision: https://reviews.llvm.org/D67564

llvm-svn: 372866
This commit is contained in:
Sanjay Patel
2019-09-25 13:14:12 +00:00
parent 12e3099921
commit dec03223a9
10 changed files with 86 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
llvm/lib/Bitcode/Reader/BitcodeReader.cpp
View File

@@ -4629,31 +4629,48 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
InstructionList.push_back(I);
break;
case bitc::FUNC_CODE_INST_PHI: { // PHI: [ty, val0,bb0, ...]
if (Record.size() < 1 || ((Record.size()-1)&1))
if (Record.size() < 1)
return error("Invalid record");
// The first record specifies the type.
FullTy = getFullyStructuredTypeByID(Record[0]);
Type *Ty = flattenPointerTypes(FullTy);
if (!Ty)
return error("Invalid record");
PHINode *PN = PHINode::Create(Ty, (Record.size()-1)/2);
// Phi arguments are pairs of records of [value, basic block].
// There is an optional final record for fast-math-flags if this phi has a
// floating-point type.
size_t NumArgs = (Record.size() - 1) / 2;
if ((Record.size() - 1) % 2 == 1 && !Ty->isFloatingPointTy())
return error("Invalid record");
PHINode *PN = PHINode::Create(Ty, NumArgs);
InstructionList.push_back(PN);
for (unsigned i = 0, e = Record.size()-1; i != e; i += 2) {
for (unsigned i = 0; i != NumArgs; i++) {
Value *V;
// With the new function encoding, it is possible that operands have
// negative IDs (for forward references). Use a signed VBR
// representation to keep the encoding small.
if (UseRelativeIDs)
V = getValueSigned(Record, 1+i, NextValueNo, Ty);
V = getValueSigned(Record, i * 2 + 1, NextValueNo, Ty);
else
V = getValue(Record, 1+i, NextValueNo, Ty);
BasicBlock *BB = getBasicBlock(Record[2+i]);
V = getValue(Record, i * 2 + 1, NextValueNo, Ty);
BasicBlock *BB = getBasicBlock(Record[i * 2 + 2]);
if (!V || !BB)
return error("Invalid record");
PN->addIncoming(V, BB);
}
I = PN;
// If there are an even number of records, the final record must be FMF.
if (Record.size() % 2 == 0) {
assert(isa<FPMathOperator>(I) && "Unexpected phi type");
FastMathFlags FMF = getDecodedFastMathFlags(Record[Record.size() - 1]);
if (FMF.any())
I->setFastMathFlags(FMF);
}
break;
}