Subzero: fix invalid arg access on Windows x86 for split variables

See the first bug I fixed related to this: 7fefd483. 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>

Subzero: fix invalid arg access on Windows x86 for split variables
3476ca34 · Antonio Maiorano · f14f6c46 · 3476ca34
Commit 3476ca34 authored Nov 04, 2020 by Antonio Maiorano
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IceTargetLoweringX86BaseImpl.h third_party/subzero/src/IceTargetLoweringX86BaseImpl.h +5 -0

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--- a/third_party/subzero/src/IceTargetLoweringX86BaseImpl.h
+++ b/third_party/subzero/src/IceTargetLoweringX86BaseImpl.h
@@ -1287,6 +1287,11 @@ void TargetX86Base<TraitsType>::addProlog(CfgNode *Node) {
    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;