AMDGPU: Avoid selecting ds_{read,write}2_b32 on SI
Summary:
To workaround a hardware issue in the (base + offset) calculation
when base is negative. The impact on code quality should be limited
since SILoadStoreOptimizer still runs afterwards and is able to
combine loads/stores based on known sign information.
This fixes visible corruption in Hitman on SI (easily reproducible
by running benchmark mode).
Change-Id: Ia178d207a5e2ac38ae7cd98b532ea2ae74704e5f
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99923
Reviewers: arsenm, mareko
Subscribers: jholewinski, kzhuravl, jvesely, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits
Differential Revision: https://reviews.llvm.org/D53160
llvm-svn: 344698
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index c2cf307..81ff640 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -6292,6 +6292,17 @@
if (NumElements > 2)
return SplitVectorLoad(Op, DAG);
+
+ // SI has a hardware bug in the LDS / GDS boounds checking: if the base
+ // address is negative, then the instruction is incorrectly treated as
+ // out-of-bounds even if base + offsets is in bounds. Split vectorized
+ // loads here to avoid emitting ds_read2_b32. We may re-combine the
+ // load later in the SILoadStoreOptimizer.
+ if (Subtarget->getGeneration() == AMDGPUSubtarget::SOUTHERN_ISLANDS &&
+ NumElements == 2 && MemVT.getStoreSize() == 8 &&
+ Load->getAlignment() < 8) {
+ return SplitVectorLoad(Op, DAG);
+ }
}
return SDValue();
}
@@ -6694,6 +6705,18 @@
if (NumElements > 2)
return SplitVectorStore(Op, DAG);
+
+ // SI has a hardware bug in the LDS / GDS boounds checking: if the base
+ // address is negative, then the instruction is incorrectly treated as
+ // out-of-bounds even if base + offsets is in bounds. Split vectorized
+ // stores here to avoid emitting ds_write2_b32. We may re-combine the
+ // store later in the SILoadStoreOptimizer.
+ if (Subtarget->getGeneration() == AMDGPUSubtarget::SOUTHERN_ISLANDS &&
+ NumElements == 2 && VT.getStoreSize() == 8 &&
+ Store->getAlignment() < 8) {
+ return SplitVectorStore(Op, DAG);
+ }
+
return SDValue();
} else {
llvm_unreachable("unhandled address space");