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[InlineCost] GetElementPtr with constant operands 

If the GEP instruction contanins only constants as its arguments,
then it should be recognized as a constant. For now, there was
also added a flag to turn off this simplification if it causes
any regressions ("disable-gep-const-evaluation") which is off
by default. Once I gather needed data of the effectiveness of
this simplification, the flag will be deleted.

Reviewers: apilipenko, davidxl, mtrofin

Reviewed By: mtrofin

Differential Revision: https://reviews.llvm.org/D81026
This commit is contained in:
Kirill Naumov 2020-06-02 19:22:41 +00:00
parent dbf7603be6
commit d48c7859fb
2 changed files with 29 additions and 0 deletions
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14
llvm/lib/Analysis/InlineCost.cpp
View File

@ -110,6 +110,10 @@ static cl::opt<bool> InlineCallerSupersetNoBuiltin(
cl::desc("Allow inlining when caller has a superset of callee's nobuiltin "
"attributes."));
static cl::opt<bool> DisableGEPConstOperand(
"disable-gep-const-evaluation", cl::Hidden, cl::init(false),
cl::desc("Disables evaluation of GetElementPtr with constant operands"));
namespace {
class InlineCostCallAnalyzer;
@ -1019,6 +1023,16 @@ bool CallAnalyzer::visitGetElementPtr(GetElementPtrInst &I) {
return true;
};
if (!DisableGEPConstOperand)
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
SmallVector<Constant *, 2> Indices;
for (unsigned int Index = 1 ; Index < COps.size() ; ++Index)
Indices.push_back(COps[Index]);
return ConstantExpr::getGetElementPtr(I.getSourceElementType(), COps[0],
Indices, I.isInBounds());
}))
return true;
if ((I.isInBounds() && canFoldInboundsGEP(I)) || IsGEPOffsetConstant(I)) {
if (SROAArg)
SROAArgValues[&I] = SROAArg;

15
llvm/test/Transforms/Inline/gep_from_constant.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: opt < %s -passes="print<inline-cost>" 2>&1 | FileCheck %s
; CHECK-LABEL: @foo
; CHECK: cost before = {{.*}}, cost after = {{.*}}, threshold before = {{.*}}, threshold after = {{.*}}, cost delta = {{.*}}, simplified to i8 addrspace(1)** getelementptr (i8 addrspace(1)*, i8 addrspace(1)** inttoptr (i64 754974720 to i8 addrspace(1)**), i64 5)
define i8 addrspace(1)** @foo(i64 %0) {
%2 = inttoptr i64 754974720 to i8 addrspace(1)**
%3 = getelementptr i8 addrspace(1)*, i8 addrspace(1)** %2, i64 %0
ret i8 addrspace(1)** %3
}
define i8 addrspace(1)** @main() {
%1 = call i8 addrspace(1)** @foo(i64 5)
ret i8 addrspace(1)** %1
}