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[InstCombine] Simplify gep (gep p, a), (b-a)

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Patch by Andrea Canciani.

Differential Revision:  https://reviews.llvm.org/D27413

llvm-svn: 292506
This commit is contained in:
Davide Italiano 2017-01-19 18:51:56 +00:00
parent 915800c7e4
commit 97a0cbad8b
2 changed files with 40 additions and 19 deletions
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32
lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -1559,27 +1559,21 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
// Replace: gep (gep %P, long B), long A, ...
// With: T = long A+B; gep %P, T, ...
//
Value *Sum;
Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
Value *GO1 = GEP.getOperand(1);
if (SO1 == Constant::getNullValue(SO1->getType())) {
Sum = GO1;
} else if (GO1 == Constant::getNullValue(GO1->getType())) {
Sum = SO1;
} else {
// If they aren't the same type, then the input hasn't been processed
// by the loop above yet (which canonicalizes sequential index types to
// intptr_t). Just avoid transforming this until the input has been
// normalized.
if (SO1->getType() != GO1->getType())
return nullptr;
// Only do the combine when GO1 and SO1 are both constants. Only in
// this case, we are sure the cost after the merge is never more than
// that before the merge.
if (!isa<Constant>(GO1) || !isa<Constant>(SO1))
return nullptr;
Sum = Builder->CreateAdd(SO1, GO1, PtrOp->getName()+".sum");
}
// If they aren't the same type, then the input hasn't been processed
// by the loop above yet (which canonicalizes sequential index types to
// intptr_t). Just avoid transforming this until the input has been
// normalized.
if (SO1->getType() != GO1->getType())
return nullptr;
Value* Sum = SimplifyAddInst(GO1, SO1, false, false, DL, &TLI, &DT, &AC);
// Only do the combine when we are sure the cost after the
// merge is never more than that before the merge.
if (Sum == nullptr)
return nullptr;
// Update the GEP in place if possible.
if (Src->getNumOperands() == 2) {

27
test/Transforms/InstCombine/getelementptr.ll
View File

@ -883,6 +883,33 @@ define %struct.C* @test46(%struct.C* %c1, %struct.C* %c2, i64 %N) {
; CHECK-NEXT: ret %struct.C* [[GEP]]
}
define i32* @test47(i32* %I, i64 %C, i64 %D) {
%sub = sub i64 %D, %C
%A = getelementptr i32, i32* %I, i64 %C
%B = getelementptr i32, i32* %A, i64 %sub
ret i32* %B
; CHECK-LABEL: @test47(
; CHECK-NEXT: %B = getelementptr i32, i32* %I, i64 %D
}
define i32* @test48(i32* %I, i64 %C, i64 %D) {
%sub = sub i64 %D, %C
%A = getelementptr i32, i32* %I, i64 %sub
%B = getelementptr i32, i32* %A, i64 %C
ret i32* %B
; CHECK-LABEL: @test48(
; CHECK-NEXT: %B = getelementptr i32, i32* %I, i64 %D
}
define i32* @test49(i32* %I, i64 %C) {
%notC = xor i64 -1, %C
%A = getelementptr i32, i32* %I, i64 %C
%B = getelementptr i32, i32* %A, i64 %notC
ret i32* %B
; CHECK-LABEL: @test49(
; CHECK-NEXT: %B = getelementptr i32, i32* %I, i64 -1
}
define i32 addrspace(1)* @ascast_0_gep(i32* %p) nounwind {
; CHECK-LABEL: @ascast_0_gep(
; CHECK-NOT: getelementptr