================
@@ -2128,6 +2129,105 @@ static void patchAndReplaceAllUsesWith(Instruction *I,
Value *Repl) {
I->replaceAllUsesWith(Repl);
}
+// split load to single byte loads and check if the value can be deduced
+//
+// Example:
+// define i32 @f(i8* %P)
+// 1: %b2 = getelementptr inbounds i8, i8* %P, i64 1
+// 2: store i8 0, i8* %b2, align 1
+// 3: store i8 0, i8* %P, align 1
+// 4: %s1 = bitcast i8* %P to i16*
+// 5: %L = load i16, i16* %s1, align 4
+//
+// The last clobbering write for the load is (3) but it doesn't cover the whole
+// read. So AnalyzeLoadAvailability would give up.
+// This function emit temporary byte-sized loads that cover the original load,
+// so that any last write covers the read. We run AnalyzeLoadAvailability on
+// each byte to try to construct the load as a constant.
+bool GVNPass::splitAndprocessLoad(LoadInst *L) {
+ if (L->isAtomic())
+ return false;
+
+ Type *LTy = L->getType();
+ if (!LTy->isIntegerTy())
+ return false;
+
+ unsigned BW = LTy->getIntegerBitWidth();
+ if (BW % 8)
+ return false;
+
+ IntegerType *ByteTy = IntegerType::getInt8Ty(LTy->getContext());
+ Type *BytePtrTy = PointerType::get(ByteTy, L->getPointerAddressSpace());
+ BitCastInst *Base = new BitCastInst(L->getPointerOperand(), BytePtrTy, "",
L);
----------------
nikic wrote:
Not necessary with opaque pointers.
https://github.com/llvm/llvm-project/pull/72364
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