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[LoopUnrollAnalyzer] Use constant folding API for loads

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Use ConstantFoldLoadFromConst() instead of a partial re-implementation.
This makes the code slightly more generic by not depending on the
exact structure of the constant.
This commit is contained in:
Nikita Popov 2024-08-27 16:16:21 +02:00
parent dfde1a7232
commit fe182ddf1f
2 changed files with 45 additions and 30 deletions
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36
llvm/lib/Analysis/LoopUnrollAnalyzer.cpp
View File

@ -13,6 +13,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoopUnrollAnalyzer.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
@ -105,7 +106,6 @@ bool UnrolledInstAnalyzer::visitLoad(LoadInst &I) {
auto AddressIt = SimplifiedAddresses.find(AddrOp);
if (AddressIt == SimplifiedAddresses.end())
return false;
const APInt &SimplifiedAddrOp = AddressIt->second.Offset;
auto *GV = dyn_cast<GlobalVariable>(AddressIt->second.Base);
// We're only interested in loads that can be completely folded to a
@ -113,37 +113,13 @@ bool UnrolledInstAnalyzer::visitLoad(LoadInst &I) {
if (!GV || !GV->hasDefinitiveInitializer() || !GV->isConstant())
return false;
ConstantDataSequential *CDS =
dyn_cast<ConstantDataSequential>(GV->getInitializer());
if (!CDS)
Constant *Res =
ConstantFoldLoadFromConst(GV->getInitializer(), I.getType(),
AddressIt->second.Offset, I.getDataLayout());
if (!Res)
return false;
// We might have a vector load from an array. FIXME: for now we just bail
// out in this case, but we should be able to resolve and simplify such
// loads.
if (CDS->getElementType() != I.getType())
return false;
unsigned ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
if (SimplifiedAddrOp.getActiveBits() > 64)
return false;
int64_t SimplifiedAddrOpV = SimplifiedAddrOp.getSExtValue();
if (SimplifiedAddrOpV < 0) {
// FIXME: For now we conservatively ignore out of bound accesses, but
// we're allowed to perform the optimization in this case.
return false;
}
uint64_t Index = static_cast<uint64_t>(SimplifiedAddrOpV) / ElemSize;
if (Index >= CDS->getNumElements()) {
// FIXME: For now we conservatively ignore out of bound accesses, but
// we're allowed to perform the optimization in this case.
return false;
}
Constant *CV = CDS->getElementAsConstant(Index);
assert(CV && "Constant expected.");
SimplifiedValues[&I] = CV;
SimplifiedValues[&I] = Res;
return true;
}

39
llvm/test/Transforms/LoopUnroll/full-unroll-heuristics-load-const.ll Normal file
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@ -0,0 +1,39 @@
; RUN: opt < %s -S -passes=loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-threshold=10 -unroll-max-percent-threshold-boost=100 | FileCheck %s -check-prefix=TEST1
; RUN: opt < %s -S -passes=loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-threshold=20 -unroll-max-percent-threshold-boost=200 | FileCheck %s -check-prefix=TEST2
; RUN: opt < %s -S -passes=loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-threshold=20 -unroll-max-percent-threshold-boost=100 | FileCheck %s -check-prefix=TEST3
; This test is a copy of full-unroll-heuristics.ll but with the constant
; wrapped in an extra struct. This should not hinder the analysis.
; If the absolute threshold is too low, we should not unroll:
; TEST1: %array_const_idx = getelementptr inbounds { [9 x i32] }, ptr @known_constant, i64 0, i32 0, i64 %iv
; Otherwise, we should:
; TEST2-NOT: %array_const_idx = getelementptr inbounds { [9 x i32] }, ptr @known_constant, i64 0, i32 0, i64 %iv
; If we do not boost threshold, the unroll will not happen:
; TEST3: %array_const_idx = getelementptr inbounds { [9 x i32] }, ptr @known_constant, i64 0, i32 0, i64 %iv
@known_constant = internal unnamed_addr constant { [9 x i32] } { [9 x i32] [i32 0, i32 -1, i32 0, i32 -1, i32 5, i32 -1, i32 0, i32 -1, i32 0] }, align 16
define i32 @foo(ptr noalias nocapture readonly %src) {
entry:
br label %loop
loop: ; preds = %loop, %entry
%iv = phi i64 [ 0, %entry ], [ %inc, %loop ]
%r = phi i32 [ 0, %entry ], [ %add, %loop ]
%arrayidx = getelementptr inbounds i32, ptr %src, i64 %iv
%src_element = load i32, ptr %arrayidx, align 4
%array_const_idx = getelementptr inbounds { [9 x i32] }, ptr @known_constant, i64 0, i32 0, i64 %iv
%const_array_element = load i32, ptr %array_const_idx, align 4
%mul = mul nsw i32 %src_element, %const_array_element
%add = add nsw i32 %mul, %r
%inc = add nuw nsw i64 %iv, 1
%exitcond86.i = icmp eq i64 %inc, 9
br i1 %exitcond86.i, label %loop.end, label %loop
loop.end: ; preds = %loop
%r.lcssa = phi i32 [ %r, %loop ]
ret i32 %r.lcssa
}