[llvm] [llvm] Add KnownBits implementations for avgFloor and avgCeil (PR #86445)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 5 09:00:50 PDT 2024
================
@@ -762,6 +762,43 @@ KnownBits KnownBits::usub_sat(const KnownBits &LHS, const KnownBits &RHS) {
return computeForSatAddSub(/*Add*/ false, /*Signed*/ false, LHS, RHS);
}
+KnownBits KnownBits::avgFloorS(const KnownBits &LHS, const KnownBits &RHS) {
+ // (C1 & C2) + (C1 ^ C2).ashr(1)
+ KnownBits andResult = LHS & RHS;
+ KnownBits xorResult = LHS ^ RHS;
+ xorResult.Zero.ashrInPlace(1);
+ xorResult.One.ashrInPlace(1);
+ return computeForAddSub(/*Add*/ true, /*Signed*/ true, andResult, xorResult);
+}
+
+KnownBits KnownBits::avgFloorU(const KnownBits &LHS, const KnownBits &RHS) {
+ // (C1 & C2) + (C1 ^ C2).lshr(1)
+ KnownBits andResult = LHS & RHS;
+ KnownBits xorResult = LHS ^ RHS;
+ xorResult.Zero.lshrInPlace(1);
+ xorResult.One.lshrInPlace(1);
+ return computeForAddSub(/*Add*/ true, /*Signed*/ false, andResult, xorResult);
+}
+
+KnownBits KnownBits::avgCeilS(const KnownBits &LHS, const KnownBits &RHS) {
+ // (C1 | C2) - (C1 ^ C2).ashr(1)
+ KnownBits andResult = LHS & RHS;
+ KnownBits xorResult = LHS ^ RHS;
+ xorResult.Zero.ashrInPlace(1);
+ xorResult.One.ashrInPlace(1);
+ return computeForAddSub(/*Add*/ false, /*Signed*/ true, andResult, xorResult);
+}
+
+KnownBits KnownBits::avgCeilU(const KnownBits &LHS, const KnownBits &RHS) {
+ // (C1 | C2) - (C1 ^ C2).lshr(1)
+ KnownBits andResult = LHS & RHS;
+ KnownBits xorResult = LHS ^ RHS;
+ xorResult.Zero.lshrInPlace(1);
+ xorResult.One.lshrInPlace(1);
+ return computeForAddSub(/*Add*/ false, /*Signed*/ false, andResult,
+ xorResult);
----------------
goldsteinn wrote:
`nuw` means that when we do `X + Y` it won't have unsigned overflow. So `X nuw+ Y >= X && X nuw+ Y >= Y` must hold. `nsw` is the same but for the signbit.
So with 8bit, `128 + 128` violates both nuw/nsw.
https://github.com/llvm/llvm-project/pull/86445
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