[llvm] [GISel][CombinerHelper] Push freeze through non-poison-producing operands (PR #90618)

[Matt Arsenault via llvm-commits]

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@@ -34,6 +34,83 @@ class GenericMachineInstr : public MachineInstr {
   static bool classof(const MachineInstr *MI) {
     return isPreISelGenericOpcode(MI->getOpcode());
   }
+
+  bool hasPoisonGeneratingFlags() const {
+    switch (getOpcode()) {
+    case TargetOpcode::G_ADD:
+    case TargetOpcode::G_SUB:
+    case TargetOpcode::G_MUL:
+    case TargetOpcode::G_SHL:
+    case TargetOpcode::G_TRUNC:
+      return getFlag(NoUWrap) || getFlag(NoSWrap);
+
+    case TargetOpcode::G_UDIV:
+    case TargetOpcode::G_SDIV:
+    case TargetOpcode::G_ASHR:
+    case TargetOpcode::G_LSHR:
+      return getFlag(IsExact);
+
+    case TargetOpcode::G_OR:
+      return getFlag(Disjoint);
+
+    case TargetOpcode::G_UITOFP:
+    case TargetOpcode::G_ZEXT:
+      return getFlag(NonNeg);
+
+    case TargetOpcode::G_FNEG:
+    case TargetOpcode::G_FADD:
+    case TargetOpcode::G_FSUB:
+    case TargetOpcode::G_FMUL:
+    case TargetOpcode::G_FDIV:
+    case TargetOpcode::G_FREM:
+    case TargetOpcode::G_FCMP:
+      return getFlag(FmNoNans) || getFlag(FmNoInfs);
+
+    default:
+      return false;
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arsenm wrote:

This should return the conservative default of true (or maybe just test if any flags are set at all). I'm also not sure we need to consider the opcodes. From construction, we won't have other flags on the MachineInstr

https://github.com/llvm/llvm-project/pull/90618