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Watch out for a constant offset cancelling out a base register, forming

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a zero. This situation arrises in Fortran code with induction variables
that start at 1 instead of 0. This fixes PR7651.

llvm-svn: 108424
This commit is contained in:
Dan Gohman 2010-07-15 15:14:45 +00:00
parent 01a2992a91
commit d75ba463e0
2 changed files with 53 additions and 2 deletions
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11
lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -2362,7 +2362,7 @@ void LSRInstance::GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx,
Formula Base) {
// TODO: For now, just add the min and max offset, because it usually isn't
// worthwhile looking at everything inbetween.
SmallVector<int64_t, 4> Worklist;
SmallVector<int64_t, 2> Worklist;
Worklist.push_back(LU.MinOffset);
if (LU.MaxOffset != LU.MinOffset)
Worklist.push_back(LU.MaxOffset);
@ -2376,7 +2376,14 @@ void LSRInstance::GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx,
F.AM.BaseOffs = (uint64_t)Base.AM.BaseOffs - *I;
if (isLegalUse(F.AM, LU.MinOffset - *I, LU.MaxOffset - *I,
LU.Kind, LU.AccessTy, TLI)) {
F.BaseRegs[i] = SE.getAddExpr(G, SE.getConstant(G->getType(), *I));
// Add the offset to the base register.
const SCEV *NewG = SE.getAddExpr(G, SE.getConstant(G->getType(), *I));
// If it cancelled out, drop the base register, otherwise update it.
if (NewG->isZero()) {
std::swap(F.BaseRegs[i], F.BaseRegs.back());
F.BaseRegs.pop_back();
} else
F.BaseRegs[i] = NewG;
(void)InsertFormula(LU, LUIdx, F);
}

44
test/CodeGen/X86/lsr-i386.ll Normal file
View File

@ -0,0 +1,44 @@
; RUN: llc -march=x86 < %s | FileCheck %s
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
target triple = "i386-pc-linux-gnu"
; PR7651
; CHECK: align
; CHECK: align
; CHECK: align
; CHECK: movl $0, (%e
; CHECK-NEXT: addl $4, %e
; CHECK-NEXT: decl %e
; CHECK-NEXT: jne
%struct.anon = type { [72 x i32], i32 }
@mp2grad_ = external global %struct.anon
define void @chomp2g_setup_(i32 %n, i32 %m) nounwind {
entry:
br label %bb1
bb1: ; preds = %bb6, %bb
%indvar11 = phi i32 [ %indvar.next12, %bb6 ], [ 0, %entry ] ; <i32> [#uses=2]
%tmp21 = add i32 %indvar11, 1 ; <i32> [#uses=1]
%t = load i32* getelementptr inbounds (%struct.anon* @mp2grad_, i32 0, i32 1)
%tmp15 = mul i32 %n, %t ; <i32> [#uses=1]
%tmp16 = add i32 %tmp21, %tmp15 ; <i32> [#uses=1]
%tmp17 = shl i32 %tmp16, 3 ; <i32> [#uses=1]
%tmp18 = add i32 %tmp17, -8 ; <i32> [#uses=1]
br label %bb2
bb2: ; preds = %bb2, %bb2.preheader
%indvar = phi i32 [ 0, %bb1 ], [ %indvar.next, %bb2 ] ; <i32> [#uses=2]
%tmp19 = add i32 %tmp18, %indvar ; <i32> [#uses=1]
%scevgep = getelementptr %struct.anon* @mp2grad_, i32 0, i32 0, i32 %tmp19 ; <i32*> [#uses=1]
store i32 0, i32* %scevgep
%indvar.next = add i32 %indvar, 1 ; <i32> [#uses=1]
%c = icmp ne i32 %indvar.next, %m
br i1 %c, label %bb2, label %bb6
bb6: ; preds = %bb2, %bb1
%indvar.next12 = add i32 %indvar11, 1 ; <i32> [#uses=1]
br label %bb1
}