diff options
Diffstat (limited to 'src/passes')
| -rw-r--r-- | src/passes/OptimizeInstructions.cpp | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp index 49100a9f4..844ed06ac 100644 --- a/src/passes/OptimizeInstructions.cpp +++ b/src/passes/OptimizeInstructions.cpp @@ -305,6 +305,17 @@ static int32_t lowBitMask(int32_t bits) { return ret >> (32 - bits); } +// checks if the input is a mask of lower bits, i.e., all 1s up to some high bit, and all zeros +// from there. returns the number of masked bits, or 0 if this is not such a mask +static uint32_t getMaskedBits(int32_t mask) { + if (mask == -1) return 32; // all the bits + if (mask == 0) return 0; // trivially not a mask + // otherwise, see if adding one turns this into a 1-bit thing, 00011111 + 1 => 00100000 + if (PopCount(mask + 1) != 1) return 0; + // this is indeed a mask + return 32 - CountLeadingZeroes(mask); +} + // performs a dynCast on the fallthrough value, i.e., looks through // too and block fallthroughs, etc. template<typename T> @@ -436,9 +447,11 @@ struct OptimizeInstructions : public WalkerPass<PostWalker<OptimizeInstructions, return binary->left; } } - } else if (mask == 1 && Properties::emitsBoolean(binary->left)) { - // (bool) & 1 does not need the outer mask - return binary->left; + } else if (auto maskedBits = getMaskedBits(mask)) { + if (getMaxBits(binary->left) <= maskedBits) { + // a mask of lower bits is not needed if we are already smaller + return binary->left; + } } } // the square of some operations can be merged |