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[InstCombine] X / (X * Y) --> 1.0 / Y 

This is similar to the instsimplify fold added with D42385 
( rL323716 )
...but this can't be in instsimplify because we're creating/morphing
a different instruction.

llvm-svn: 324927
This commit is contained in:
Sanjay Patel 2018-02-12 19:39:21 +00:00
parent ee4257f676
commit 4a4f35f324
2 changed files with 12 additions and 6 deletions
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10
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -1523,6 +1523,16 @@ Instruction *InstCombiner::visitFDiv(BinaryOperator &I) {
return &I;
}
// X / (X * Y) --> 1.0 / Y
// Reassociate to (X / X -> 1.0) is legal when NaNs are not allowed.
// We can ignore the possibility that X is infinity because INF/INF is NaN.
if (I.hasNoNaNs() && I.hasAllowReassoc() &&
match(Op1, m_c_FMul(m_Specific(Op0), m_Value(Y)))) {
I.setOperand(0, ConstantFP::get(I.getType(), 1.0));
I.setOperand(1, Y);
return &I;
}
return nullptr;
}

8
llvm/test/Transforms/InstCombine/fdiv.ll
View File

@ -83,13 +83,11 @@ define float @fdiv_fneg_fneg_fast(float %x, float %y) {
ret float %div
}
; FIXME:
; X / (X * Y) --> 1.0 / Y
define float @div_factor(float %x, float %y) {
; CHECK-LABEL: @div_factor(
; CHECK-NEXT: [[M:%.*]] = fmul float [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[D:%.*]] = fdiv reassoc nnan float [[X]], [[M]]
; CHECK-NEXT: [[D:%.*]] = fdiv reassoc nnan float 1.000000e+00, [[Y:%.*]]
; CHECK-NEXT: ret float [[D]]
;
%m = fmul float %x, %y
@ -110,14 +108,12 @@ define float @div_factor_too_strict(float %x, float %y) {
ret float %d
}
; FIXME:
; Commute, verify vector types, and show that we are not dropping extra FMF.
; X / (Y * X) --> 1.0 / Y
define <2 x float> @div_factor_commute(<2 x float> %x, <2 x float> %y) {
; CHECK-LABEL: @div_factor_commute(
; CHECK-NEXT: [[M:%.*]] = fmul <2 x float> [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[D:%.*]] = fdiv reassoc nnan ninf nsz <2 x float> [[X]], [[M]]
; CHECK-NEXT: [[D:%.*]] = fdiv reassoc nnan ninf nsz <2 x float> <float 1.000000e+00, float 1.000000e+00>, [[Y:%.*]]
; CHECK-NEXT: ret <2 x float> [[D]]
;
%m = fmul <2 x float> %y, %x