R600: Recommit 199842: Add work-around for the CF stack entry HW bug

The unit test is now disabled on non-asserts builds.

The CF stack can be corrupted if you use CF_ALU_PUSH_BEFORE,
CF_ALU_ELSE_AFTER, CF_ALU_BREAK, or CF_ALU_CONTINUE when the number of
sub-entries on the stack is greater than or equal to the stack entry
size and sub-entries modulo 4 is either 0 or 3 (on cedar the bug is
present when number of sub-entries module 8 is either 7 or 0)

We choose to be conservative and always apply the work-around when the
number of sub-enries is greater than or equal to the stack entry size,
so that we can safely over-allocate the stack when we are unsure of the
stack allocation rules.

reviewed-by: Vincent Lejeune <vljn at ovi.com>
llvm-svn: 199905

llvm/lib/Target/R600/AMDGPU.td

@@ -63,6 +63,11 @@ def FeatureCaymanISA : SubtargetFeature<"caymanISA",
         "true",
         "Use Cayman ISA">;
 
+def FeatureCFALUBug : SubtargetFeature<"cfalubug",
+        "CFALUBug",
+        "true",
+        "GPU has CF_ALU bug">;
+
 class SubtargetFeatureFetchLimit <string Value> :
                           SubtargetFeature <"fetch"#Value,
         "TexVTXClauseSize",

llvm/lib/Target/R600/AMDGPUSubtarget.cpp

@@ -39,6 +39,7 @@ AMDGPUSubtarget::AMDGPUSubtarget(StringRef TT, StringRef CPU, StringRef FS) :
   EnableIRStructurizer = true;
   EnableIfCvt = true;
   WavefrontSize = 0;
+  CFALUBug = false;
   ParseSubtargetFeatures(GPU, FS);
   DevName = GPU;
 }
@@ -97,6 +98,11 @@ AMDGPUSubtarget::getStackEntrySize() const {
   }
 }
 bool
+AMDGPUSubtarget::hasCFAluBug() const {
+  assert(getGeneration() <= NORTHERN_ISLANDS);
+  return CFALUBug;
+}
+bool
 AMDGPUSubtarget::isTargetELF() const {
   return false;
 }

llvm/lib/Target/R600/AMDGPUSubtarget.h

@@ -52,6 +52,7 @@ private:
   bool EnableIRStructurizer;
   bool EnableIfCvt;
   unsigned WavefrontSize;
+  bool CFALUBug;
 
   InstrItineraryData InstrItins;
 
@@ -71,6 +72,7 @@ public:
   bool isIfCvtEnabled() const;
   unsigned getWavefrontSize() const;
   unsigned getStackEntrySize() const;
+  bool hasCFAluBug() const;
 
   virtual bool enableMachineScheduler() const {
     return getGeneration() <= NORTHERN_ISLANDS;

llvm/lib/Target/R600/Processors.td

@@ -46,13 +46,15 @@ def : Proc<"rv770",      R600_VLIW5_Itin,
 //===----------------------------------------------------------------------===//
 
 def : Proc<"cedar",      R600_VLIW5_Itin,
-    [FeatureEvergreen, FeatureVertexCache, FeatureWavefrontSize32]>;
+    [FeatureEvergreen, FeatureVertexCache, FeatureWavefrontSize32,
+     FeatureCFALUBug]>;
 
 def : Proc<"redwood",    R600_VLIW5_Itin,
-    [FeatureEvergreen, FeatureVertexCache, FeatureWavefrontSize64]>;
+    [FeatureEvergreen, FeatureVertexCache, FeatureWavefrontSize64,
+     FeatureCFALUBug]>;
 
 def : Proc<"sumo",       R600_VLIW5_Itin,
-    [FeatureEvergreen, FeatureWavefrontSize64]>;
+    [FeatureEvergreen, FeatureWavefrontSize64, FeatureCFALUBug]>;
 
 def : Proc<"juniper",    R600_VLIW5_Itin,
     [FeatureEvergreen, FeatureVertexCache, FeatureWavefrontSize64]>;
@@ -66,13 +68,13 @@ def : Proc<"cypress",    R600_VLIW5_Itin,
 //===----------------------------------------------------------------------===//
 
 def : Proc<"barts",      R600_VLIW5_Itin,
-    [FeatureNorthernIslands, FeatureVertexCache]>;
+    [FeatureNorthernIslands, FeatureVertexCache, FeatureCFALUBug]>;
 
 def : Proc<"turks",      R600_VLIW5_Itin,
-    [FeatureNorthernIslands, FeatureVertexCache]>;
+    [FeatureNorthernIslands, FeatureVertexCache, FeatureCFALUBug]>;
 
 def : Proc<"caicos",     R600_VLIW5_Itin,
-    [FeatureNorthernIslands]>;
+    [FeatureNorthernIslands, FeatureCFALUBug]>;
 
 def : Proc<"cayman",     R600_VLIW4_Itin,
     [FeatureNorthernIslands, FeatureFP64, FeatureCaymanISA]>;

llvm/lib/Target/R600/R600ControlFlowFinalizer.cpp

@@ -73,6 +73,44 @@ bool CFStack::branchStackContains(CFStack::StackItem Item) {
   return false;
 }
 
+bool CFStack::requiresWorkAroundForInst(unsigned Opcode) {
+  if (Opcode == AMDGPU::CF_ALU_PUSH_BEFORE && ST.hasCaymanISA() &&
+      getLoopDepth() > 1)
+    return true;
+
+  if (!ST.hasCFAluBug())
+    return false;
+
+  switch(Opcode) {
+  default: return false;
+  case AMDGPU::CF_ALU_PUSH_BEFORE:
+  case AMDGPU::CF_ALU_ELSE_AFTER:
+  case AMDGPU::CF_ALU_BREAK:
+  case AMDGPU::CF_ALU_CONTINUE:
+    if (CurrentSubEntries == 0)
+      return false;
+    if (ST.getWavefrontSize() == 64) {
+      // We are being conservative here.  We only require this work-around if
+      // CurrentSubEntries > 3 &&
+      // (CurrentSubEntries % 4 == 3 || CurrentSubEntries % 4 == 0)
+      //
+      // We have to be conservative, because we don't know for certain that
+      // our stack allocation algorithm for Evergreen/NI is correct.  Applying this
+      // work-around when CurrentSubEntries > 3 allows us to over-allocate stack
+      // resources without any problems.
+      return CurrentSubEntries > 3;
+    } else {
+      assert(ST.getWavefrontSize() == 32);
+      // We are being conservative here.  We only require the work-around if
+      // CurrentSubEntries > 7 &&
+      // (CurrentSubEntries % 8 == 7 || CurrentSubEntries % 8 == 0)
+      // See the comment on the wavefront size == 64 case for why we are
+      // being conservative.
+      return CurrentSubEntries > 7;
+    }
+  }
+}
+
 unsigned CFStack::getSubEntrySize(CFStack::StackItem Item) {
   switch(Item) {
   default:
@@ -472,9 +510,12 @@ public:
         if (MI->getOpcode() == AMDGPU::CF_ALU)
           LastAlu.back() = MI;
         I++;
+        bool RequiresWorkAround =
+            CFStack.requiresWorkAroundForInst(MI->getOpcode());
         switch (MI->getOpcode()) {
         case AMDGPU::CF_ALU_PUSH_BEFORE:
-          if (ST.hasCaymanISA() && CFStack.getLoopDepth() > 1) {
+          if (RequiresWorkAround) {
+            DEBUG(dbgs() << "Applying bug work-around for ALU_PUSH_BEFORE\n");
             BuildMI(MBB, MI, MBB.findDebugLoc(MI), TII->get(AMDGPU::CF_PUSH_EG))
                 .addImm(CfCount + 1)
                 .addImm(1);

llvm/test/CodeGen/R600/cf-stack-bug.ll

@@ -0,0 +1,227 @@
+; RUN: llc -march=r600 -mcpu=redwood -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=BUG64 --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=sumo -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=BUG64 --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=barts -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=BUG64 --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=turks -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=BUG64 --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=caicos -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=BUG64 --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=cedar -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=BUG32 --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=juniper -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=NOBUG --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=cypress -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=NOBUG --check-prefix=FUNC
+; RUN: llc -march=r600 -mcpu=cayman -debug-only=r600cf %s -o - 2>&1 | FileCheck %s --check-prefix=NOBUG --check-prefix=FUNC
+
+; REQUIRES: asserts
+
+; We are currently allocating 2 extra sub-entries on Evergreen / NI for
+; non-WQM push instructions if we change this to 1, then we will need to
+; add one level of depth to each of these tests.
+
+; BUG64-NOT: Applying bug work-around
+; BUG32-NOT: Applying bug work-around
+; NOBUG-NOT: Applying bug work-around
+; FUNC-LABEL: @nested3
+define void @nested3(i32 addrspace(1)* %out, i32 %cond) {
+entry:
+  %0 = icmp sgt i32 %cond, 0
+  br i1 %0, label %if.1, label %end
+
+if.1:
+  %1 = icmp sgt i32 %cond, 10
+  br i1 %1, label %if.2, label %if.store.1
+
+if.store.1:
+  store i32 1, i32 addrspace(1)* %out
+  br label %end
+
+if.2:
+  %2 = icmp sgt i32 %cond, 20
+  br i1 %2, label %if.3, label %if.2.store
+
+if.2.store:
+  store i32 2, i32 addrspace(1)* %out
+  br label %end
+
+if.3:
+  store i32 3, i32 addrspace(1)* %out
+  br label %end
+
+end:
+  ret void
+}
+
+; BUG64: Applying bug work-around
+; BUG32-NOT: Applying bug work-around
+; NOBUG-NOT: Applying bug work-around
+; FUNC-LABEL: @nested4
+define void @nested4(i32 addrspace(1)* %out, i32 %cond) {
+entry:
+  %0 = icmp sgt i32 %cond, 0
+  br i1 %0, label %if.1, label %end
+
+if.1:
+  %1 = icmp sgt i32 %cond, 10
+  br i1 %1, label %if.2, label %if.1.store
+
+if.1.store:
+  store i32 1, i32 addrspace(1)* %out
+  br label %end
+
+if.2:
+  %2 = icmp sgt i32 %cond, 20
+  br i1 %2, label %if.3, label %if.2.store
+
+if.2.store:
+  store i32 2, i32 addrspace(1)* %out
+  br label %end
+
+if.3:
+  %3 = icmp sgt i32 %cond, 30
+  br i1 %3, label %if.4, label %if.3.store
+
+if.3.store:
+  store i32 3, i32 addrspace(1)* %out
+  br label %end
+
+if.4:
+  store i32 4, i32 addrspace(1)* %out
+  br label %end
+
+end:
+  ret void
+}
+
+; BUG64: Applying bug work-around
+; BUG32-NOT: Applying bug work-around
+; NOBUG-NOT: Applying bug work-around
+; FUNC-LABEL: @nested7
+define void @nested7(i32 addrspace(1)* %out, i32 %cond) {
+entry:
+  %0 = icmp sgt i32 %cond, 0
+  br i1 %0, label %if.1, label %end
+
+if.1:
+  %1 = icmp sgt i32 %cond, 10
+  br i1 %1, label %if.2, label %if.1.store
+
+if.1.store:
+  store i32 1, i32 addrspace(1)* %out
+  br label %end
+
+if.2:
+  %2 = icmp sgt i32 %cond, 20
+  br i1 %2, label %if.3, label %if.2.store
+
+if.2.store:
+  store i32 2, i32 addrspace(1)* %out
+  br label %end
+
+if.3:
+  %3 = icmp sgt i32 %cond, 30
+  br i1 %3, label %if.4, label %if.3.store
+
+if.3.store:
+  store i32 3, i32 addrspace(1)* %out
+  br label %end
+
+if.4:
+  %4 = icmp sgt i32 %cond, 40
+  br i1 %4, label %if.5, label %if.4.store
+
+if.4.store:
+  store i32 4, i32 addrspace(1)* %out
+  br label %end
+
+if.5:
+  %5 = icmp sgt i32 %cond, 50
+  br i1 %5, label %if.6, label %if.5.store
+
+if.5.store:
+  store i32 5, i32 addrspace(1)* %out
+  br label %end
+
+if.6:
+  %6 = icmp sgt i32 %cond, 60
+  br i1 %6, label %if.7, label %if.6.store
+
+if.6.store:
+  store i32 6, i32 addrspace(1)* %out
+  br label %end
+
+if.7:
+  store i32 7, i32 addrspace(1)* %out
+  br label %end
+
+end:
+  ret void
+}
+
+; BUG64: Applying bug work-around
+; BUG32: Applying bug work-around
+; NOBUG-NOT: Applying bug work-around
+; FUNC-LABEL: @nested8
+define void @nested8(i32 addrspace(1)* %out, i32 %cond) {
+entry:
+  %0 = icmp sgt i32 %cond, 0
+  br i1 %0, label %if.1, label %end
+
+if.1:
+  %1 = icmp sgt i32 %cond, 10
+  br i1 %1, label %if.2, label %if.1.store
+
+if.1.store:
+  store i32 1, i32 addrspace(1)* %out
+  br label %end
+
+if.2:
+  %2 = icmp sgt i32 %cond, 20
+  br i1 %2, label %if.3, label %if.2.store
+
+if.2.store:
+  store i32 2, i32 addrspace(1)* %out
+  br label %end
+
+if.3:
+  %3 = icmp sgt i32 %cond, 30
+  br i1 %3, label %if.4, label %if.3.store
+
+if.3.store:
+  store i32 3, i32 addrspace(1)* %out
+  br label %end
+
+if.4:
+  %4 = icmp sgt i32 %cond, 40
+  br i1 %4, label %if.5, label %if.4.store
+
+if.4.store:
+  store i32 4, i32 addrspace(1)* %out
+  br label %end
+
+if.5:
+  %5 = icmp sgt i32 %cond, 50
+  br i1 %5, label %if.6, label %if.5.store
+
+if.5.store:
+  store i32 5, i32 addrspace(1)* %out
+  br label %end
+
+if.6:
+  %6 = icmp sgt i32 %cond, 60
+  br i1 %6, label %if.7, label %if.6.store
+
+if.6.store:
+  store i32 6, i32 addrspace(1)* %out
+  br label %end
+
+if.7:
+  %7 = icmp sgt i32 %cond, 70
+  br i1 %7, label %if.8, label %if.7.store
+
+if.7.store:
+  store i32 7, i32 addrspace(1)* %out
+  br label %end
+
+if.8:
+  store i32 8, i32 addrspace(1)* %out
+  br label %end
+
+end:
+  ret void
+}