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[InstCombine] Optimize icmp of inc/dec at RHS

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Allow LLVM to optimize the sequence like the following:

  %inc = add nsw i32 %i, 1
  %cmp = icmp slt %n, %inc

into:

  %cmp = icmp sle i32 %n, %i

The case is not handled previously due to the complexity of compuation of %n.
Hence, LLVM cannot swap operands of icmp accordingly.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250746 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Michael Liao 2015-10-19 22:08:14 +00:00
parent f792618d1c
commit 2949a6ae04
2 changed files with 60 additions and 0 deletions
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20
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -3426,6 +3426,26 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
match(B, m_One()))
return new ICmpInst(CmpInst::ICMP_SGE, A, Op1);
// icmp sgt X, (Y + -1) -> icmp sge X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGT &&
match(D, m_AllOnes()))
return new ICmpInst(CmpInst::ICMP_SGE, Op0, C);
// icmp sle X, (Y + -1) -> icmp slt X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLE &&
match(D, m_AllOnes()))
return new ICmpInst(CmpInst::ICMP_SLT, Op0, C);
// icmp sge X, (Y + 1) -> icmp sgt X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGE &&
match(D, m_One()))
return new ICmpInst(CmpInst::ICMP_SGT, Op0, C);
// icmp slt X, (Y + 1) -> icmp sle X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLT &&
match(D, m_One()))
return new ICmpInst(CmpInst::ICMP_SLE, Op0, C);
// if C1 has greater magnitude than C2:
// icmp (X + C1), (Y + C2) -> icmp (X + C3), Y
// s.t. C3 = C1 - C2

40
test/Transforms/InstCombine/icmp.ll
View File

@ -1632,3 +1632,43 @@ entry:
%cmp580 = icmp ule i16 mul (i16 zext (i8 ptrtoint (i1 (i16)* @f10 to i8) to i16), i16 zext (i8 ptrtoint (i1 (i16)* @f10 to i8) to i16)), %p
ret i1 %cmp580
}
; CHECK-LABEL: @cmp_sgt_rhs_dec
; CHECK-NOT: sub
; CHECK: icmp sge
define i1 @cmp_sgt_rhs_dec(float %x, i32 %i) {
%conv = fptosi float %x to i32
%dec = sub nsw i32 %i, 1
%cmp = icmp sgt i32 %conv, %dec
ret i1 %cmp
}
; CHECK-LABEL: @cmp_sle_rhs_dec
; CHECK-NOT: sub
; CHECK: icmp slt
define i1 @cmp_sle_rhs_dec(float %x, i32 %i) {
%conv = fptosi float %x to i32
%dec = sub nsw i32 %i, 1
%cmp = icmp sle i32 %conv, %dec
ret i1 %cmp
}
; CHECK-LABEL: @cmp_sge_rhs_inc
; CHECK-NOT: add
; CHECK: icmp sgt
define i1 @cmp_sge_rhs_inc(float %x, i32 %i) {
%conv = fptosi float %x to i32
%inc = add nsw i32 %i, 1
%cmp = icmp sge i32 %conv, %inc
ret i1 %cmp
}
; CHECK-LABEL: @cmp_slt_rhs_inc
; CHECK-NOT: add
; CHECK: icmp sle
define i1 @cmp_slt_rhs_inc(float %x, i32 %i) {
%conv = fptosi float %x to i32
%inc = add nsw i32 %i, 1
%cmp = icmp slt i32 %conv, %inc
ret i1 %cmp
}