Commit 821290a1 authored by Julian Seward's avatar Julian Seward
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Bug 1823857 - part 1: Code::lookupTrap: lift an invariant expression out of a hot loop. r=rhunt. 

Code::lookupTrap has

  uint32_t target = ((uint8_t*)pc) - segment(t).base();

in a loop in which it is invariant.  This patch lifts it out of the loop since
the clang++ 15.0.7 does not appear to do so, even at -O2.  Reduces (host)
instruction count by around 10% on some artificial small wasm-gc tests.

Differential Revision: https://phabricator.services.mozilla.com/D173275
parent 471df3ea

js/src/wasm/WasmCode.cpp

+3 −5
Original line number Diff line number Diff line
@@ -1049,17 +1049,15 @@ struct TrapSitePCOffset { 


bool Code::lookupTrap(void* pc, Trap* trapOut, BytecodeOffset* bytecode) const {

  for (Tier t : tiers()) {

    uint32_t target = ((uint8_t*)pc) - segment(t).base();

    const TrapSiteVectorArray& trapSitesArray = metadata(t).trapSites;

    for (Trap trap : MakeEnumeratedRange(Trap::Limit)) {

      const TrapSiteVector& trapSites = trapSitesArray[trap];



      uint32_t target = ((uint8_t*)pc) - segment(t).base();

      size_t lowerBound = 0;

      size_t upperBound = trapSites.length();



      size_t match;

      if (BinarySearch(TrapSitePCOffset(trapSites), lowerBound, upperBound,

                       target, &match)) {

      if (BinarySearch(TrapSitePCOffset(trapSites), 0, upperBound, target,

                       &match)) {

        MOZ_ASSERT(segment(t).containsCodePC(pc));

        *trapOut = trap;

        *bytecode = trapSites[match].bytecode;