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When the visitSub method was split into visitSub and visitFSub, this xform was

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added to the FSub version. However, the original version of this xform guarded
against doing this for floating point (!Op0->getType()->isFPOrFPVector()).

This is causing LLVM to perform incorrect xforms for code like:

void func(double *rhi, double *rlo, double xh, double xl, double yh, double yl){
  double mh, ml;
  double c = 134217729.0;
  double up, u1, u2, vp, v1, v2;
        
  up = xh*c;
  u1 = (xh - up) + up;
  u2 = xh - u1;
        
  vp = yh*c;
  v1 = (yh - vp) + vp;
  v2 = yh - v1;
        
  mh = xh*yh;
  ml = (((u1*v1 - mh) + (u1*v2)) + (u2*v1)) + (u2*v2);
  ml += xh*yl + xl*yh;
        
  *rhi = mh + ml;
  *rlo = (mh - (*rhi)) + ml;
}

The last line was optimized away, but rl is intended to be the difference
between the infinitely precise result of mh + ml and after it has been rounded
to double precision.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93369 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2010-01-13 23:23:17 +00:00
parent edd1cc78d2
commit 22f3b9faac
2 changed files with 39 additions and 11 deletions
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11
lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -736,16 +736,5 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
if (Value *V = dyn_castFNegVal(Op1)) if (Value *V = dyn_castFNegVal(Op1))
return BinaryOperator::CreateFAdd(Op0, V); return BinaryOperator::CreateFAdd(Op0, V);
if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1)) {
if (Op1I->getOpcode() == Instruction::FAdd) {
if (Op1I->getOperand(0) == Op0) // X-(X+Y) == -Y
return BinaryOperator::CreateFNeg(Op1I->getOperand(1),
I.getName());
else if (Op1I->getOperand(1) == Op0) // X-(Y+X) == -Y
return BinaryOperator::CreateFNeg(Op1I->getOperand(0),
I.getName());
}
}
return 0; return 0;
} }

39
test/Transforms/InstCombine/fsub-fadd.ll Normal file
View File

@ -0,0 +1,39 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
; <rdar://problem/7530098>
define void @func(double* %rhi, double* %rlo, double %xh, double %xl, double %yh, double %yl) nounwind ssp {
entry:
%"alloca point" = bitcast i32 0 to i32 ; <i32> [#uses=0]
%tmp = fmul double %xh, 0x41A0000002000000 ; <double> [#uses=2]
%tmp1 = fsub double %xh, %tmp ; <double> [#uses=1]
%tmp2 = fadd double %tmp1, %tmp ; <double> [#uses=3]
%tmp3 = fsub double %xh, %tmp2 ; <double> [#uses=2]
%tmp4 = fmul double %yh, 0x41A0000002000000 ; <double> [#uses=2]
%tmp5 = fsub double %yh, %tmp4 ; <double> [#uses=1]
%tmp6 = fadd double %tmp5, %tmp4 ; <double> [#uses=3]
%tmp7 = fsub double %yh, %tmp6 ; <double> [#uses=2]
%tmp8 = fmul double %xh, %yh ; <double> [#uses=3]
%tmp9 = fmul double %tmp2, %tmp6 ; <double> [#uses=1]
%tmp10 = fsub double %tmp9, %tmp8 ; <double> [#uses=1]
%tmp11 = fmul double %tmp2, %tmp7 ; <double> [#uses=1]
%tmp12 = fadd double %tmp10, %tmp11 ; <double> [#uses=1]
%tmp13 = fmul double %tmp3, %tmp6 ; <double> [#uses=1]
%tmp14 = fadd double %tmp12, %tmp13 ; <double> [#uses=1]
%tmp15 = fmul double %tmp3, %tmp7 ; <double> [#uses=1]
%tmp16 = fadd double %tmp14, %tmp15 ; <double> [#uses=1]
%tmp17 = fmul double %xh, %yl ; <double> [#uses=1]
%tmp18 = fmul double %xl, %yh ; <double> [#uses=1]
%tmp19 = fadd double %tmp17, %tmp18 ; <double> [#uses=1]
%tmp20 = fadd double %tmp19, %tmp16 ; <double> [#uses=2]
%tmp21 = fadd double %tmp8, %tmp20 ; <double> [#uses=1]
store double %tmp21, double* %rhi, align 8
%tmp22 = load double* %rhi, align 8 ; <double> [#uses=1]
%tmp23 = fsub double %tmp8, %tmp22 ; <double> [#uses=1]
%tmp24 = fadd double %tmp23, %tmp20 ; <double> [#uses=1]
; CHECK: %tmp23 = fsub double %tmp8, %tmp21
; CHECK: %tmp24 = fadd double %tmp23, %tmp20
store double %tmp24, double* %rlo, align 8
ret void
}