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Use value ranges to fold ext(trunc) in SCEV when possible.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124062 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2011-01-23 06:20:19 +00:00
parent 54cdad97eb
commit 630d85a78c
2 changed files with 68 additions and 0 deletions
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34
lib/Analysis/ScalarEvolution.cpp
View File

@ -898,6 +898,23 @@ const SCEV *ScalarEvolution::getZeroExtendExpr(const SCEV *Op,
void *IP = 0;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
// zext(trunc(x)) --> zext(x) or x or trunc(x)
if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
// It's possible the bits taken off by the truncate were all zero bits. If
// so, we should be able to simplify this further.
const SCEV *X = ST->getOperand();
ConstantRange CR = getUnsignedRange(X);
unsigned OrigBits = CR.getBitWidth();
unsigned TruncBits = getTypeSizeInBits(ST->getType());
unsigned NewBits = getTypeSizeInBits(Ty);
if (CR.truncate(TruncBits).zeroExtend(NewBits).contains(
CR.zextOrTrunc(NewBits))) {
if (NewBits > OrigBits) return getZeroExtendExpr(X, Ty);
if (NewBits < OrigBits) return getTruncateExpr(X, Ty);
return X;
}
}
// If the input value is a chrec scev, and we can prove that the value
// did not overflow the old, smaller, value, we can zero extend all of the
// operands (often constants). This allows analysis of something like
@ -1039,6 +1056,23 @@ const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op,
if (isKnownNonNegative(Op))
return getZeroExtendExpr(Op, Ty);
// sext(trunc(x)) --> sext(x) or x or trunc(x)
if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
// It's possible the bits taken off by the truncate were all sign bits. If
// so, we should be able to simplify this further.
const SCEV *X = ST->getOperand();
ConstantRange CR = getSignedRange(X);
unsigned OrigBits = CR.getBitWidth();
unsigned TruncBits = getTypeSizeInBits(ST->getType());
unsigned NewBits = getTypeSizeInBits(Ty);
if (CR.truncate(TruncBits).signExtend(NewBits).contains(
CR.sextOrTrunc(NewBits))) {
if (NewBits > OrigBits) return getSignExtendExpr(X, Ty);
if (NewBits < OrigBits) return getTruncateExpr(X, Ty);
return X;
}
}
// If the input value is a chrec scev, and we can prove that the value
// did not overflow the old, smaller, value, we can sign extend all of the
// operands (often constants). This allows analysis of something like

34
test/Analysis/ScalarEvolution/fold.ll
View File

@ -22,3 +22,37 @@ define i8 @test3(i8 %x) {
; CHECK: (3 * %x)
ret i8 %C
}
define void @test4(i32 %x) {
entry:
%0 = icmp sge i32 %x, 0
br i1 %0, label %loop, label %exit
loop:
%A = phi i32 [0, %entry], [%I, %loop]
%rand = icmp sgt i32 %A, 10
%Z = select i1 %rand, i32 %A, i32 10
%B = trunc i32 %Z to i16
%C = sext i16 %B to i30
; CHECK: %C =
; CHECK-NEXT: (trunc i32 (10 smax {0,+,1}<%loop>) to i30)
%D = sext i16 %B to i32
; CHECK: %D =
; CHECK-NEXT: (10 smax {0,+,1}<%loop>)
%E = sext i16 %B to i34
; CHECK: %E =
; CHECK-NEXT: (zext i32 (10 smax {0,+,1}<%loop>) to i34)
%F = zext i16 %B to i30
; CHECK: %F =
; CHECK-NEXT: (trunc i32 (10 smax {0,+,1}<%loop>) to i30
%G = zext i16 %B to i32
; CHECK: %G =
; CHECK-NEXT: (10 smax {0,+,1}<%loop>)
%H = zext i16 %B to i34
; CHECK: %H =
; CHECK-NEXT: (zext i32 (10 smax {0,+,1}<%loop>) to i34)
%I = add i32 %A, 1
%1 = icmp ne i32 %A, 20
br i1 %1, label %loop, label %exit
exit:
ret void
}