[llvm] [AMDGPU] Fix VOP3P NEG fold to check the use opcode, not the def (PR #219728)

[Matt Arsenault via llvm-commits]

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@@ -5163,9 +5164,34 @@ calcNextStatus(std::pair<Register, SrcStatus> Curr,
   return std::nullopt;
 }
 
-/// This is used to control valid status that current MI supports. For example,
-/// non floating point intrinsic such as @llvm.amdgcn.sdot2 does not support NEG
-/// bit on VOP3P.
+/// Packed integer VOP3P opcodes ignore NEG/NEG_HI, so folding a G_FNEG into
+/// them would silently drop the negation.
+static bool usesFPSrcMods(const MachineInstr &MI) {
+  unsigned Opc = MI.getOpcode();
+  if (isPreISelGenericFloatingPointOpcode(Opc))
+    return true;
+
+  // To re-audit, collect the direct parent of each "(VOP3PMods" in
+  // AMDGPUGenGlobalISel.inc.
+  switch (Opc) {
+  case AMDGPU::G_AMDGPU_CLAMP:
+  case AMDGPU::G_AMDGPU_FMIN3:
+  case AMDGPU::G_AMDGPU_FMAX3:
+  case AMDGPU::G_AMDGPU_FMINIMUM3:
+  case AMDGPU::G_AMDGPU_FMAXIMUM3:
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arsenm wrote:

These cases don't have any VOP3P packed instructions?

https://github.com/llvm/llvm-project/pull/219728