Broaden AMDGPU m013 suppression

Author: asdadqwe

amdgpu/README.md

@@ -69,7 +69,7 @@ rediscovering the same issue.
 | `FUZZX_ALLOW_M010_I16_SEXT_CLEAR_XOR=1` | unset | Re-enable the `i16` sign-extended identity clear xor shape for [m010](known-miscompiles/m010-i16-sext-clear-xor/NOTES.md). |
 | `FUZZX_ALLOW_M011_I8_SEXT_CLEAR_XOR=1` | unset | Re-enable the `i8` sign-extended identity clear xor shape for [m011](known-miscompiles/m011-i8-sext-clear-xor/NOTES.md). |
 | `FUZZX_ALLOW_M012_ADD_SHL_LADDER=1` | unset | Alias to re-enable the broader `add/shl` ladder shape for [m012](known-miscompiles/m012-add-shl-ladder/NOTES.md). |
-| `FUZZX_ALLOW_M013_PRIVATE_MEMORY_FSHL=1` | unset | Re-enable five-or-more private-memory/funnel-shift ops for [m013](known-miscompiles/m013-private-memory-fshl/NOTES.md). |
+| `FUZZX_ALLOW_M013_PRIVATE_MEMORY_FSHL=1` | unset | Re-enable three-or-more private-memory/funnel-shift ops for [m013](known-miscompiles/m013-private-memory-fshl/NOTES.md). |
 
 ## Layout
 

amdgpu/fuzzers/llvm-amdgpu-diff/llvm_amdgpu_diff_fuzzer.cpp

@@ -274,10 +274,10 @@ bool isVectorOp(const Op &O) { return O.Kind == 21 || O.Kind == 22; }
 
 bool isPrivateMemoryOp(const Op &O) { return O.Kind == 53 || O.Kind == 58; }
 
-bool hasFivePrivateMemoryOps(ArrayRef<Op> Ops) {
+bool hasThreePrivateMemoryOps(ArrayRef<Op> Ops) {
   unsigned Count = 0;
   for (const Op &O : Ops) {
-    if (isPrivateMemoryOp(O) && ++Count >= 5)
+    if (isPrivateMemoryOp(O) && ++Count >= 3)
       return true;
   }
   return false;
@@ -355,7 +355,7 @@ Program makeProgram(const uint8_t *Data, size_t Size) {
         P.Ops.back().Kind = 11;
       }
     }
-    if (!AllowM013 && hasFivePrivateMemoryOps(P.Ops))
+    if (!AllowM013 && hasThreePrivateMemoryOps(P.Ops))
       P.Ops.back().Kind = 54;
   }
   P.UseStructuredCFG = P.Ops.size() >= 4 && (BS.next8() & 1);

amdgpu/known-miscompiles/m013-private-memory-fshl/NOTES.md

@@ -88,6 +88,12 @@ ad 12 ef 8a
 
 ## Fuzzer Suppression
 
-The directed C++ fuzzer now caps generated private-memory ops at four by
+The directed C++ fuzzer now caps generated private-memory ops at two by
 default. Set `FUZZX_ALLOW_M013_PRIVATE_MEMORY_FSHL=1` to re-enable the
-five-or-more private-memory/funnel-shift shape when replaying this fuzzer input.
+three-or-more private-memory/funnel-shift shape when replaying this fuzzer
+input.
+
+A later structured-CFG variant with original fuzzer input SHA-1
+`ea7a9d7c7d69ca16f1a670c154a71ed4f71f6e56` showed that three private-memory
+ops are enough to hit the same scratch-stack issue, so the suppression is
+intentionally broader than the five-copy linear reduced testcase.