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[CVP] Remove a masking operation if range information implies it's a noop

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This is really a known bits style transformation, but known bits isn't context sensitive. The particular case which comes up happens to involve a range which allows range based reasoning to eliminate the mask pattern, so handle that case specifically in CVP.

InstCombine likes to generate the mask-by-low-bits pattern when widening an arithmetic expression which includes a zext in the middle.

Differential Revision: https://reviews.llvm.org/D68811

llvm-svn: 374506
This commit is contained in:
Philip Reames 2019-10-11 03:48:56 +00:00
parent c8b84d5441
commit 044f56dbf9
4 changed files with 155 additions and 3 deletions
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27
lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
View File

@ -63,6 +63,7 @@ STATISTIC(NumUDivs, "Number of udivs whose width was decreased");
STATISTIC(NumAShrs, "Number of ashr converted to lshr");
STATISTIC(NumSRems, "Number of srem converted to urem");
STATISTIC(NumSExt, "Number of sext converted to zext");
STATISTIC(NumAnd, "Number of ands removed");
STATISTIC(NumOverflows, "Number of overflow checks removed");
STATISTIC(NumSaturating,
"Number of saturating arithmetics converted to normal arithmetics");
@ -700,6 +701,29 @@ static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI) {
return Changed;
}
static bool processAnd(BinaryOperator *BinOp, LazyValueInfo *LVI) {
if (BinOp->getType()->isVectorTy())
return false;
// Pattern match (and lhs, C) where C includes a superset of bits which might
// be set in lhs. This is a common truncation idiom created by instcombine.
BasicBlock *BB = BinOp->getParent();
Value *LHS = BinOp->getOperand(0);
ConstantInt *RHS = dyn_cast<ConstantInt>(BinOp->getOperand(1));
if (!RHS || !RHS->getValue().isMask())
return false;
ConstantRange LRange = LVI->getConstantRange(LHS, BB, BinOp);
if (!LRange.getUnsignedMax().ule(RHS->getValue()))
return false;
BinOp->replaceAllUsesWith(LHS);
BinOp->eraseFromParent();
NumAnd++;
return true;
}
static Constant *getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI) {
if (Constant *C = LVI->getConstant(V, At->getParent(), At))
return C;
@ -774,6 +798,9 @@ static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
case Instruction::Sub:
BBChanged |= processBinOp(cast<BinaryOperator>(II), LVI);
break;
case Instruction::And:
BBChanged |= processAnd(cast<BinaryOperator>(II), LVI);
break;
}
}

127
test/Transforms/CorrelatedValuePropagation/and.ll Normal file
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@ -0,0 +1,127 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -correlated-propagation -S | FileCheck %s
define i32 @test(i32 %a) {
; CHECK-LABEL: @test(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[A:%.*]], 128
; CHECK-NEXT: br i1 [[CMP]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: ret i32 [[A]]
; CHECK: exit:
; CHECK-NEXT: ret i32 -1
;
entry:
%cmp = icmp ult i32 %a, 128
br i1 %cmp, label %continue, label %exit
continue:
%and = and i32 %a, 255
ret i32 %and
exit:
ret i32 -1
}
define i32 @test2(i32 %a) {
; CHECK-LABEL: @test2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[A:%.*]], 256
; CHECK-NEXT: br i1 [[CMP]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: ret i32 [[A]]
; CHECK: exit:
; CHECK-NEXT: ret i32 -1
;
entry:
%cmp = icmp ult i32 %a, 256
br i1 %cmp, label %continue, label %exit
continue:
%and = and i32 %a, 255
ret i32 %and
exit:
ret i32 -1
}
define i32 @test3(i32 %a) {
; CHECK-LABEL: @test3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[A:%.*]], 256
; CHECK-NEXT: br i1 [[CMP]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: ret i32 [[A]]
; CHECK: exit:
; CHECK-NEXT: ret i32 -1
;
entry:
%cmp = icmp ult i32 %a, 256
br i1 %cmp, label %continue, label %exit
continue:
%and = and i32 %a, 1023
ret i32 %and
exit:
ret i32 -1
}
define i32 @neg1(i32 %a) {
; CHECK-LABEL: @neg1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp ule i32 [[A:%.*]], 256
; CHECK-NEXT: br i1 [[CMP]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: [[AND:%.*]] = and i32 [[A]], 255
; CHECK-NEXT: ret i32 [[AND]]
; CHECK: exit:
; CHECK-NEXT: ret i32 -1
;
entry:
%cmp = icmp ule i32 %a, 256
br i1 %cmp, label %continue, label %exit
continue:
%and = and i32 %a, 255
ret i32 %and
exit:
ret i32 -1
}
define i32 @neg2(i32 %a) {
; CHECK-LABEL: @neg2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[A:%.*]], 513
; CHECK-NEXT: br i1 [[CMP]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: [[AND:%.*]] = and i32 [[A]], 255
; CHECK-NEXT: ret i32 [[AND]]
; CHECK: exit:
; CHECK-NEXT: ret i32 -1
;
entry:
%cmp = icmp ult i32 %a, 513
br i1 %cmp, label %continue, label %exit
continue:
%and = and i32 %a, 255
ret i32 %and
exit:
ret i32 -1
}
define i32 @neg3(i32 %a) {
; CHECK-LABEL: @neg3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[A:%.*]], 256
; CHECK-NEXT: br i1 [[CMP]], label [[CONTINUE:%.*]], label [[EXIT:%.*]]
; CHECK: continue:
; CHECK-NEXT: [[AND:%.*]] = and i32 [[A]], 254
; CHECK-NEXT: ret i32 [[AND]]
; CHECK: exit:
; CHECK-NEXT: ret i32 -1
;
entry:
%cmp = icmp ult i32 %a, 256
br i1 %cmp, label %continue, label %exit
continue:
%and = and i32 %a, 254
ret i32 %and
exit:
ret i32 -1
}

1
test/Transforms/CorrelatedValuePropagation/overflows.ll
View File

@ -1023,7 +1023,6 @@ define i1 @smul_and_cmp(i32 %x, i32 %y) #0 {
; CHECK-NEXT: [[MUL:%.*]] = extractvalue { i32, i1 } [[TMP0]], 0
; CHECK-NEXT: br label [[CONT3:%.*]]
; CHECK: cont3:
; CHECK-NEXT: [[CMP5:%.*]] = and i1 true, true
; CHECK-NEXT: br label [[OUT]]
; CHECK: out:
; CHECK-NEXT: ret i1 true

3
test/Transforms/CorrelatedValuePropagation/range.ll
View File

@ -745,10 +745,9 @@ target93:
define i1 @test17_i1(i1 %a) {
; CHECK-LABEL: @test17_i1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[C:%.*]] = and i1 [[A:%.*]], true
; CHECK-NEXT: br label [[DISPATCH:%.*]]
; CHECK: dispatch:
; CHECK-NEXT: br i1 [[A]], label [[TRUE:%.*]], label [[DISPATCH]]
; CHECK-NEXT: br i1 [[A:%.*]], label [[TRUE:%.*]], label [[DISPATCH]]
; CHECK: true:
; CHECK-NEXT: ret i1 true
;