[ValueTracking] Compute range for abs without nsw
This is a small followup to D59511. The code that was moved into
computeConstantRange() there is a bit overly conversative: If the
abs is not nsw, it does not compute any range. However, abs without
nsw still has a well-defined contiguous unsigned range from 0 to
SIGNED_MIN. This is a lot less useful than the usual 0 to SIGNED_MAX
range, but if we're already here we might as well specify it...
Differential Revision: https://reviews.llvm.org/D59563
llvm-svn: 356586
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 99d6010..52328b1 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -5673,14 +5673,15 @@
unsigned BitWidth = SI.getType()->getScalarSizeInBits();
- // matchSelectPattern() returns the negation part of an abs pattern in RHS.
- // If the negate has an NSW flag, abs(INT_MIN) is undefined. Without that
- // constraint, we can't make a contiguous range for the result of abs.
- if (R.Flavor == SelectPatternFlavor::SPF_ABS &&
- cast<Instruction>(RHS)->hasNoSignedWrap()) {
- // The result of abs(X) is >= 0 (with nsw).
+ if (R.Flavor == SelectPatternFlavor::SPF_ABS) {
+ // If the negation part of the abs (in RHS) has the NSW flag,
+ // then the result of abs(X) is [0..SIGNED_MAX],
+ // otherwise it is [0..SIGNED_MIN], as -SIGNED_MIN == SIGNED_MIN.
Lower = APInt::getNullValue(BitWidth);
- Upper = APInt::getSignedMaxValue(BitWidth) + 1;
+ if (cast<Instruction>(RHS)->hasNoSignedWrap())
+ Upper = APInt::getSignedMaxValue(BitWidth) + 1;
+ else
+ Upper = APInt::getSignedMinValue(BitWidth) + 1;
return;
}