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[InstCombine] Fold fcmp into select (#86482)
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This patch simplifies `fcmp (select Cond, C1, C2), C3` patterns in
ceres:
Alive2: https://alive2.llvm.org/ce/z/fWh_sD
```
define i1 @src(double %x) {
  %cmp1 = fcmp ord double %x, 0.000000e+00
  %sel = select i1 %cmp1, double 0xFFFFFFFFFFFFFFFF, double 0.000000e+00
  %cmp2 = fcmp oeq double %sel, 0.000000e+00
  ret i1 %cmp2
}

define i1 @tgt(double %x) {
  %cmp1 = fcmp uno double %x, 0.000000e+00
  ret i1 %cmp1
}

```
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@dtcxzyw
dtcxzyw committed Apr 23, 2024
1 parent b817451 commit 9fb7a73
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Showing 3 changed files with 125 additions and 4 deletions.
2 changes: 2 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8052,6 +8052,8 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
m_Select(m_Value(), m_Value(X), m_FNeg(m_Deferred(X)))) ||
match(LHSI, m_Select(m_Value(), m_FNeg(m_Value(X)), m_Deferred(X)))))
return replaceOperand(I, 0, X);
if (Instruction *NV = FoldOpIntoSelect(I, cast<SelectInst>(LHSI)))
return NV;
break;
case Instruction::PHI:
if (Instruction *NV = foldOpIntoPhi(I, cast<PHINode>(LHSI)))
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120 changes: 120 additions & 0 deletions llvm/test/Transforms/InstCombine/fcmp-select.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

declare void @use(i1)
declare void @usef64(double)

; X == 42.0 ? X : 42.0 --> 42.0

Expand Down Expand Up @@ -148,3 +149,122 @@ define i1 @fcmp_ogt_select(i1 %cond, float %a, float %b) {
%res = fcmp ogt float %lhs, %rhs
ret i1 %res
}

define i1 @test_fcmp_select_const_const(double %x) {
; CHECK-LABEL: @test_fcmp_select_const_const(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp uno double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: ret i1 [[CMP1]]
;
%cmp1 = fcmp ord double %x, 0.000000e+00
%sel = select i1 %cmp1, double 0xFFFFFFFFFFFFFFFF, double 0.000000e+00
%cmp2 = fcmp oeq double %sel, 0.000000e+00
ret i1 %cmp2
}

define i1 @test_fcmp_select_var_const(double %x, double %y) {
; CHECK-LABEL: @test_fcmp_select_var_const(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp ule double [[X:%.*]], 0x3E80000000000000
; CHECK-NEXT: [[TMP1:%.*]] = fcmp olt double [[Y:%.*]], 0x3E80000000000000
; CHECK-NEXT: [[CMP2:%.*]] = select i1 [[CMP1]], i1 true, i1 [[TMP1]]
; CHECK-NEXT: ret i1 [[CMP2]]
;
%cmp1 = fcmp ogt double %x, 0x3E80000000000000
%sel = select i1 %cmp1, double %y, double 0.000000e+00
%cmp2 = fcmp olt double %sel, 0x3E80000000000000
ret i1 %cmp2
}

define i1 @test_fcmp_select_var_const_fmf(double %x, double %y) {
; CHECK-LABEL: @test_fcmp_select_var_const_fmf(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp ule double [[X:%.*]], 0x3E80000000000000
; CHECK-NEXT: [[TMP1:%.*]] = fcmp nnan olt double [[Y:%.*]], 0x3E80000000000000
; CHECK-NEXT: [[CMP2:%.*]] = select i1 [[CMP1]], i1 true, i1 [[TMP1]]
; CHECK-NEXT: ret i1 [[CMP2]]
;
%cmp1 = fcmp ogt double %x, 0x3E80000000000000
%sel = select i1 %cmp1, double %y, double 0.000000e+00
%cmp2 = fcmp nnan olt double %sel, 0x3E80000000000000
ret i1 %cmp2
}

define <2 x i1> @test_fcmp_select_const_const_vec(<2 x double> %x) {
; CHECK-LABEL: @test_fcmp_select_const_const_vec(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp uno <2 x double> [[X:%.*]], zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[CMP1]]
;
%cmp1 = fcmp ord <2 x double> %x, zeroinitializer
%sel = select <2 x i1> %cmp1, <2 x double> <double 0xFFFFFFFFFFFFFFFF, double 0xFFFFFFFFFFFFFFFF>, <2 x double> zeroinitializer
%cmp2 = fcmp oeq <2 x double> %sel, zeroinitializer
ret <2 x i1> %cmp2
}

; Don't break clamp idioms

define double @test_fcmp_select_clamp(double %x) {
; CHECK-LABEL: @test_fcmp_select_clamp(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp ogt double [[X:%.*]], 9.000000e-01
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], double 9.000000e-01, double [[X]]
; CHECK-NEXT: [[CMP2:%.*]] = fcmp olt double [[SEL1]], 5.000000e-01
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], double 5.000000e-01, double [[SEL1]]
; CHECK-NEXT: ret double [[SEL2]]
;
%cmp1 = fcmp ogt double %x, 9.000000e-01
%sel1 = select i1 %cmp1, double 9.000000e-01, double %x
%cmp2 = fcmp olt double %sel1, 5.000000e-01
%sel2 = select i1 %cmp2, double 5.000000e-01, double %sel1
ret double %sel2
}

; Don't break fmin/fmax idioms

define double @test_fcmp_select_maxnum(double %x) {
; CHECK-LABEL: @test_fcmp_select_maxnum(
; CHECK-NEXT: [[SEL1:%.*]] = call nnan nsz double @llvm.maxnum.f64(double [[X:%.*]], double 1.000000e+00)
; CHECK-NEXT: [[SEL2:%.*]] = call nnan nsz double @llvm.minnum.f64(double [[SEL1]], double 2.550000e+02)
; CHECK-NEXT: ret double [[SEL2]]
;
%cmp1 = fcmp ogt double %x, 1.0
%sel1 = select nnan nsz i1 %cmp1, double %x, double 1.0
%cmp2 = fcmp olt double %sel1, 255.0
%sel2 = select nnan nsz i1 %cmp2, double %sel1, double 255.0
ret double %sel2
}

define i1 @test_fcmp_select_const_const_multiuse(double %x) {
; CHECK-LABEL: @test_fcmp_select_const_const_multiuse(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp ord double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP1]], double 0xFFFFFFFFFFFFFFFF, double 0.000000e+00
; CHECK-NEXT: call void @usef64(double [[SEL]])
; CHECK-NEXT: [[CMP2:%.*]] = fcmp oeq double [[SEL]], 0.000000e+00
; CHECK-NEXT: ret i1 [[CMP2]]
;
%cmp1 = fcmp ord double %x, 0.000000e+00
%sel = select i1 %cmp1, double 0xFFFFFFFFFFFFFFFF, double 0.000000e+00
call void @usef64(double %sel)
%cmp2 = fcmp oeq double %sel, 0.000000e+00
ret i1 %cmp2
}

define i1 @test_fcmp_select_const_const_unordered(double %x) {
; CHECK-LABEL: @test_fcmp_select_const_const_unordered(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp ord double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: ret i1 [[CMP1]]
;
%cmp1 = fcmp uno double %x, 0.000000e+00
%sel = select i1 %cmp1, double 0xFFFFFFFFFFFFFFFF, double 0.000000e+00
%cmp2 = fcmp oeq double %sel, 0.000000e+00
ret i1 %cmp2
}

define i1 @test_fcmp_select_var_const_unordered(double %x, double %y) {
; CHECK-LABEL: @test_fcmp_select_var_const_unordered(
; CHECK-NEXT: [[CMP1:%.*]] = fcmp ult double [[X:%.*]], 0x3E80000000000000
; CHECK-NEXT: [[TMP1:%.*]] = fcmp ugt double [[Y:%.*]], 0x3E80000000000000
; CHECK-NEXT: [[CMP2:%.*]] = select i1 [[CMP1]], i1 [[TMP1]], i1 false
; CHECK-NEXT: ret i1 [[CMP2]]
;
%cmp1 = fcmp ult double %x, 0x3E80000000000000
%sel = select i1 %cmp1, double %y, double 0.000000e+00
%cmp2 = fcmp ugt double %sel, 0x3E80000000000000
ret i1 %cmp2
}
7 changes: 3 additions & 4 deletions llvm/test/Transforms/InstCombine/select-select.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -18,11 +18,10 @@ define float @foo1(float %a) {

define float @foo2(float %a) {
; CHECK-LABEL: @foo2(
; CHECK-NEXT: [[B:%.*]] = fcmp ogt float [[A:%.*]], 0.000000e+00
; CHECK-NEXT: [[C:%.*]] = select i1 [[B]], float [[A]], float 0.000000e+00
; CHECK-NEXT: [[B:%.*]] = fcmp ule float [[C:%.*]], 0.000000e+00
; CHECK-NEXT: [[D:%.*]] = fcmp olt float [[C]], 1.000000e+00
; CHECK-NEXT: [[E:%.*]] = select i1 [[B]], float [[A]], float 0.000000e+00
; CHECK-NEXT: [[F:%.*]] = select i1 [[D]], float [[E]], float 1.000000e+00
; CHECK-NEXT: [[E:%.*]] = select i1 [[D]], float [[C]], float 1.000000e+00
; CHECK-NEXT: [[F:%.*]] = select i1 [[B]], float 0.000000e+00, float [[E]]
; CHECK-NEXT: ret float [[F]]
;
%b = fcmp ogt float %a, 0.0
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