diff options
Diffstat (limited to 'source/slang/slang-ir-dce.cpp')
| -rw-r--r-- | source/slang/slang-ir-dce.cpp | 26 |
1 files changed, 17 insertions, 9 deletions
diff --git a/source/slang/slang-ir-dce.cpp b/source/slang/slang-ir-dce.cpp index 0b89baf64..9578bf5e5 100644 --- a/source/slang/slang-ir-dce.cpp +++ b/source/slang/slang-ir-dce.cpp @@ -75,7 +75,7 @@ struct DeadCodeEliminationContext } } - IRInst* getUndefInst() + IRInst* getUnitPoisonVal() { if (!undefInst) { @@ -84,7 +84,7 @@ struct DeadCodeEliminationContext builder.setInsertBefore(firstChild); else builder.setInsertInto(module->getModuleInst()); - undefInst = Slang::getUndefInst(builder, module); + undefInst = Slang::getUnitPoisonVal(builder, module); } return undefInst; } @@ -109,12 +109,20 @@ struct DeadCodeEliminationContext // markInstAsLive(root); - // Ensure there is a global undef inst that is always alive. - // This undef inst will be used to fill in weak-referencing uses - // whose used value is marked as dead and eliminated. - // We always make sure this undef inst is available to prevent - // infiniate oscilating loops. - markInstAsLive(getUndefInst()); + // We will use a single instruction representing an undefined + // value (using the `poison` instruction) as the replacement + // for any lingering uses of a value that is marked as dead + // (those uses logically represent "weak" references to the + // original value, since they didn't cause it to be kept alive). + // + // We need to make sure that this unique undefined value is + // treated as live, because if it is allowed to be removed then + // the compiler can get into an infinite oscillating loop where + // we determine that this instruction is not live and thus try + // to remove it and replace it with... a new instruction that + // is exactly like it. + // + markInstAsLive(getUnitPoisonVal()); // Marking the module as live should have // seeded our work list, so we can now start @@ -233,7 +241,7 @@ struct DeadCodeEliminationContext // if (inst->hasUses()) { - inst->replaceUsesWith(getUndefInst()); + inst->replaceUsesWith(getUnitPoisonVal()); } if (inst->getOp() == kIROp_Param) |