diff options
Diffstat (limited to 'src/passes/OptimizeInstructions.cpp')
| -rw-r--r-- | src/passes/OptimizeInstructions.cpp | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp index 2ca670f89..2b0a95fc7 100644 --- a/src/passes/OptimizeInstructions.cpp +++ b/src/passes/OptimizeInstructions.cpp @@ -468,9 +468,9 @@ struct OptimizeInstructions if (auto* binary = curr->dynCast<Binary>()) { if (auto* ext = Properties::getAlmostSignExt(binary)) { - Index extraShifts; - auto bits = Properties::getAlmostSignExtBits(binary, extraShifts); - if (extraShifts == 0) { + Index extraLeftShifts; + auto bits = Properties::getAlmostSignExtBits(binary, extraLeftShifts); + if (extraLeftShifts == 0) { if (auto* load = Properties::getFallthrough(ext, getPassOptions(), features) ->dynCast<Load>()) { @@ -488,11 +488,17 @@ struct OptimizeInstructions } } } - // if the sign-extend input cannot have a sign bit, we don't need it - // we also don't need it if it already has an identical-sized sign - // extend - if (Bits::getMaxBits(ext, this) + extraShifts < bits || - isSignExted(ext, bits)) { + // We can in some cases remove part of a sign extend, that is, + // (x << A) >> B => x << (A - B) + // If the sign-extend input cannot have a sign bit, we don't need it. + if (Bits::getMaxBits(ext, this) + extraLeftShifts < bits) { + return removeAlmostSignExt(binary); + } + // We also don't need it if it already has an identical-sized sign + // extend applied to it. That is, if it is already a sign-extended + // value, then another sign extend will do nothing. We do need to be + // careful of the extra shifts, though. + if (isSignExted(ext, bits) && extraLeftShifts == 0) { return removeAlmostSignExt(binary); } } else if (binary->op == EqInt32 || binary->op == NeInt32) { |