================
@@ -8309,6 +8316,74 @@ bool
CodeGenPrepare::optimizeExtractElementInst(Instruction *Inst) {
return false;
}
+// Given the instruction Inst, rewrite its discriminator operand Disc if it is
+// a PHI node with all incoming values being @llvm.ptrauth.blend(addr, imm)
+// with the same immediate modifier.
+bool CodeGenPrepare::optimizePtrauthInst(Instruction *Inst, Value *Disc) {
+ // GVN PRE, SimplifyCFG and possibly other passes may hoist or sink the call
+ // to @llvm.ptrauth.blend intrinsic, introducing multiple duplicate call
+ // instructions hidden behind a PHI node.
+ //
+ // To enforce the specific immediate modifier being blended into the
+ // discriminator even if the other, address component was reloaded from the
+ // stack, the AArch64 backend defines a number of pseudo instructions
+ // representing auth, sign and other operations. These pseudo instructions
+ // have separate register and immediate operands absorbing the arguments of
+ // blend intrinsic in case of a common `op(ptr, key_id, blend(addr, imm))`
+ // code pattern.
+ //
+ // To help the instruction selector, this function detects the discriminators
+ // represented by a PHI node with all incoming values being `blend`s with
+ // the same integer operand - each such discriminator is rewritten as a
single
+ // blend, whose address operand is a PHI node.
+
+ PHINode *P = dyn_cast<PHINode>(Disc);
+ if (!P)
+ return false;
+
+ // Checks if V is blend(something, imm), returns imm if it is.
+ auto GetImmModifier = [](Value *V) -> std::optional<uint64_t> {
+ auto *II = dyn_cast<IntrinsicInst>(V);
+ if (!II || II->getIntrinsicID() != Intrinsic::ptrauth_blend)
+ return std::nullopt;
+ auto *ImmModifier = dyn_cast<ConstantInt>(II->getArgOperand(1));
+ if (!ImmModifier)
----------------
ojhunt wrote:
I was about to ask "when is there no second argument" because apparently
reading `dyn_cast` was too hard for me :D
but is this limitation strictly required? is the concern spilling a variable
extra discriminator along the lines of?
(pseudo ir)
```
...
%a = call i64 @llvm.ptrauth.blend(i64 %addr.1, i64 %v1)
...
%b= call i64 @llvm.ptrauth.blend(i64 %addr.2, i64 %v1)
...
%r = phi(%a,%b)
```
getting turned into
```
%v1 = ...
; spill %v1
...
; load %v1
%x = phi(%a, %b)
%r = call i64 @llvm.ptrauth.blend(i64 %x, i64 %v1)
```
https://github.com/llvm/llvm-project/pull/150226
_______________________________________________
llvm-branch-commits mailing list
llvm-branch-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
