Subzero: fix invalid arg access on Windows x86 for split variables
See the first bug I fixed related to this: 7fefd4833b96e0eea1478d4a3751bb7662504bfc.
That bug fix ensured that arguments are accessed relative to 'ebp'
rather than 'esp' on Windows x86. However, when an arg Variable gets
split (see LocalVariableSplitter), the new Variable that's linked to the
original arg Variable must also use 'ebp' in the same way. This is now
fixed by making sure to set its "isArg" state to match that of the
"linked stack root" Variable at the same time as we set its
"stackOffset" in the same way. Thus, when stackVarToAsmOperand is called
during emitIAS, split Variables are properly addressed using the correct
frame pointer.
See the detailed design doc:
https://docs.google.com/document/d/1IBsWg2V9_arWGYkpuwlKdne4lkA6XwSQ8fp99l8BmnA
This fixes the intermittent crash reported here:
https://bugs.chromium.org/p/angleproject/issues/detail?id=4482#c15
Bug: angleproject:4482
Change-Id: Ibc089f3a5b9a44f40f130a3db8656011212d2983
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/50008
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/third_party/subzero/src/IceTargetLoweringX86BaseImpl.h b/third_party/subzero/src/IceTargetLoweringX86BaseImpl.h
index ab90fad..935a3d8 100644
--- a/third_party/subzero/src/IceTargetLoweringX86BaseImpl.h
+++ b/third_party/subzero/src/IceTargetLoweringX86BaseImpl.h
@@ -1287,6 +1287,11 @@
const Variable *Root = Var->getLinkedToStackRoot();
assert(Root != nullptr);
Var->setStackOffset(Root->getStackOffset());
+
+ // If the stack root variable is an arg, make this variable an arg too so
+ // that stackVarToAsmOperand uses the correct base pointer (e.g. ebp on
+ // x86).
+ Var->setIsArg(Root->getIsArg());
}
this->HasComputedFrame = true;
