commit 3a84c8e25251b961bf91f713b5175f834aaa7bef
author Nicolas Capens <capn@google.com> Tue Jul 13 15:56:24 2021 -0400
committer Nicolas Capens <nicolascapens@google.com> Mon Jul 19 20:29:12 2021 +0000
tree fcd862c37affd38c8490cb9acdb1dff8c2fb3dfc
parent 5059719664731ff36ca52cc20fa805c44e9ebdd6

Fix RequiredStackAlignment initialization

sizeof(Traits::WordType) evaluates to obtaining the size of the numeric
value of the IceType_i32 or IceType_i64 enum. Because enums default to
being constants with an underlying type of 'int', this becomes 4 for
both the x86-32 and x86-64 backends, while 8 was intended for the
latter.

A misaligned stack may have a significant performance impact.

Note that an even greater stack alignment might be required, as both the
Microsoft and System V x64 ABI require 16-byte alignment. This change
only addresses the obvious semantics bug.

Bug: b/193550986
Change-Id: If33c0a10d73c50bfb1bbc25f16acb97b3575e27a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/55809
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Sean Risser <srisser@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

third_party/subzero/src/IceTargetLoweringX8632.h

diff --git a/third_party/subzero/src/IceTargetLoweringX8632.h b/third_party/subzero/src/IceTargetLoweringX8632.h
index a012d17..8272ebe 100644
--- a/third_party/subzero/src/IceTargetLoweringX8632.h
+++ b/third_party/subzero/src/IceTargetLoweringX8632.h
@@ -874,7 +874,7 @@
   void findRMW();
 
   bool IsEbpBasedFrame = false;
-  size_t RequiredStackAlignment = sizeof(Traits::WordType);
+  size_t RequiredStackAlignment = sizeof(int32_t); // 4 bytes
   size_t SpillAreaSizeBytes = 0;
   size_t FixedAllocaSizeBytes = 0;
   size_t FixedAllocaAlignBytes = 0;

third_party/subzero/src/IceTargetLoweringX8664.h

diff --git a/third_party/subzero/src/IceTargetLoweringX8664.h b/third_party/subzero/src/IceTargetLoweringX8664.h
index 738ddae..78074d2 100644
--- a/third_party/subzero/src/IceTargetLoweringX8664.h
+++ b/third_party/subzero/src/IceTargetLoweringX8664.h
@@ -868,7 +868,7 @@
   void findRMW();
 
   bool IsEbpBasedFrame = false;
-  size_t RequiredStackAlignment = sizeof(Traits::WordType);
+  size_t RequiredStackAlignment = sizeof(int64_t); // 8 bytes
   size_t SpillAreaSizeBytes = 0;
   size_t FixedAllocaSizeBytes = 0;
   size_t FixedAllocaAlignBytes = 0;