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[InstCombine] Fold icmp ugt/ult (udiv i32 C2, X), C1. 

This patch adds support for two optimizations:
icmp ugt (udiv C2, X), C1 -> icmp ule X, C2/(C1+1)
icmp ult (udiv C2, X), C1 -> icmp ugt X, C2/C1

Differential Revision: http://reviews.llvm.org/D20123

llvm-svn: 269109
This commit is contained in:
Chad Rosier 2016-05-10 20:22:09 +00:00
parent 7347fce4c3
commit 4e6cda2db5
2 changed files with 112 additions and 3 deletions
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24
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2093,8 +2093,28 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
break;
}
case Instruction::SDiv:
case Instruction::UDiv:
if (ConstantInt *DivLHS = dyn_cast<ConstantInt>(LHSI->getOperand(0))) {
Value *X = LHSI->getOperand(1);
APInt C1 = RHS->getValue();
APInt C2 = DivLHS->getValue();
assert(C2 != 0 && "udiv 0, X should have been simplified already.");
// (icmp ugt (udiv C2, X), C1) -> (icmp ule X, C2/(C1+1))
if (ICI.getPredicate() == ICmpInst::ICMP_UGT) {
assert(!C1.isMaxValue() &&
"icmp ugt X, UINT_MAX should have been simplified already.");
return new ICmpInst(ICmpInst::ICMP_ULE, X,
ConstantInt::get(X->getType(), C2.udiv(C1 + 1)));
}
// (icmp ult (udiv C2, X), C1) -> (icmp ugt X, C2/C1)
if (ICI.getPredicate() == ICmpInst::ICMP_ULT) {
assert(C1 != 0 && "icmp ult X, 0 should have been simplified already.");
return new ICmpInst(ICmpInst::ICMP_UGT, X,
ConstantInt::get(X->getType(), C2.udiv(C1)));
}
}
// fall-through
case Instruction::SDiv:
// Fold: icmp pred ([us]div X, C1), C2 -> range test
// Fold this div into the comparison, producing a range check.
// Determine, based on the divide type, what the range is being
@ -2105,8 +2125,6 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
if (Instruction *R = FoldICmpDivCst(ICI, cast<BinaryOperator>(LHSI),
DivRHS))
return R;
// FIXME: Handle (icmp ugt (udiv i32 CI2, A), CI) and
// (icmp ult (udiv i32 CI2, A), CI).
break;
case Instruction::Sub: {

91
llvm/test/Transforms/InstCombine/compare-udiv.ll
View File

@ -39,3 +39,94 @@ define i1 @test5(i32 %d) {
%cmp1 = icmp ne i32 %div, 0
ret i1 %cmp1
}
; CHECK-LABEL: @test6
; CHECK: %cmp1 = icmp ult i32 %d, 6
define i1 @test6(i32 %d) {
%div = udiv i32 5, %d
%cmp1 = icmp ugt i32 %div, 0
ret i1 %cmp1
}
; (icmp ugt (udiv C1, X), C1) -> false.
; CHECK-LABEL: @test7
; CHECK: ret i1 false
define i1 @test7(i32 %d) {
%div = udiv i32 8, %d
%cmp1 = icmp ugt i32 %div, 8
ret i1 %cmp1
}
; CHECK-LABEL: @test8
; CHECK: %cmp1 = icmp ult i32 %d, 2
define i1 @test8(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ugt i32 %div, 3
ret i1 %cmp1
}
; CHECK-LABEL: @test9
; CHECK: %cmp1 = icmp ult i32 %d, 2
define i1 @test9(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ugt i32 %div, 2
ret i1 %cmp1
}
; CHECK-LABEL: @test10
; CHECK: %cmp1 = icmp ult i32 %d, 3
define i1 @test10(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ugt i32 %div, 1
ret i1 %cmp1
}
; CHECK-LABEL: @test11
; CHECK: %cmp1 = icmp ugt i32 %d, 4
define i1 @test11(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ult i32 %div, 1
ret i1 %cmp1
}
; CHECK-LABEL: @test12
; CHECK: %cmp1 = icmp ugt i32 %d, 2
define i1 @test12(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ult i32 %div, 2
ret i1 %cmp1
}
; CHECK-LABEL: @test13
; CHECK: %cmp1 = icmp ugt i32 %d, 1
define i1 @test13(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ult i32 %div, 3
ret i1 %cmp1
}
; CHECK-LABEL: @test14
; CHECK: %cmp1 = icmp ugt i32 %d, 1
define i1 @test14(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ult i32 %div, 4
ret i1 %cmp1
}
; icmp ugt X, UINT_MAX -> false.
; CHECK-LABEL: @test15
; CHECK: ret i1 false
define i1 @test15(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ugt i32 %div, -1
ret i1 %cmp1
}
; icmp ult X, UINT_MAX -> true.
; CHECK-LABEL: @test16
; CHECK: ret i1 true
define i1 @test16(i32 %d) {
%div = udiv i32 4, %d
%cmp1 = icmp ult i32 %div, -1
ret i1 %cmp1
}