[llvm] [GlobalIsel] Combine freeze (PR #93239)

[Matt Arsenault via llvm-commits]

Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>
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In-Reply-To: <llvm.org/llvm/llvm-project/pull/93239 at github.com>


================
@@ -1745,18 +1778,55 @@ static bool canCreateUndefOrPoison(Register Reg, const MachineRegisterInfo &MRI,
                                    UndefPoisonKind Kind) {
   MachineInstr *RegDef = MRI.getVRegDef(Reg);
 
-  if (auto *GMI = dyn_cast<GenericMachineInstr>(RegDef)) {
-    if (ConsiderFlagsAndMetadata && includesPoison(Kind) &&
-        GMI->hasPoisonGeneratingFlags())
-      return true;
-  } else {
-    // Conservatively return true.
-    return true;
-  }
+  if (ConsiderFlagsAndMetadata && includesPoison(Kind))
+    if (auto *GMI = dyn_cast<GenericMachineInstr>(RegDef))
+      if (GMI->hasPoisonGeneratingFlags())
+        return true;
 
+  // Check whether opcode is a poison/undef-generating operation.
   switch (RegDef->getOpcode()) {
   case TargetOpcode::G_FREEZE:
+  case TargetOpcode::G_BUILD_VECTOR:
+  case TargetOpcode::G_CONSTANT_FOLD_BARRIER:
     return false;
+  case TargetOpcode::G_SHL:
+  case TargetOpcode::G_ASHR:
+  case TargetOpcode::G_LSHR:
+    return includesPoison(Kind) &&
+           !shiftAmountKnownInRange(RegDef->getOperand(2).getReg(), MRI);
+  case TargetOpcode::G_FPTOSI:
+  case TargetOpcode::G_FPTOUI:
+    // fptosi/ui yields poison if the resulting value does not fit in the
+    // destination type.
+    return true;
+  case TargetOpcode::G_CTLZ:
+  case TargetOpcode::G_CTTZ:
+  case TargetOpcode::G_ABS:
+  case TargetOpcode::G_CTPOP:
+  case TargetOpcode::G_BSWAP:
+  case TargetOpcode::G_BITREVERSE:
+  case TargetOpcode::G_FSHL:
+  case TargetOpcode::G_FSHR:
+  case TargetOpcode::G_SMAX:
+  case TargetOpcode::G_SMIN:
+  case TargetOpcode::G_UMAX:
+  case TargetOpcode::G_UMIN:
+  case TargetOpcode::G_PTRMASK:
+  case TargetOpcode::G_SADDO:
+  case TargetOpcode::G_SSUBO:
+  case TargetOpcode::G_UADDO:
+  case TargetOpcode::G_USUBO:
+  case TargetOpcode::G_SMULO:
+  case TargetOpcode::G_UMULO:
+  case TargetOpcode::G_SADDSAT:
+  case TargetOpcode::G_UADDSAT:
+  case TargetOpcode::G_SSUBSAT:
+  case TargetOpcode::G_USUBSAT:
+    return false;
+  case TargetOpcode::G_SSHLSAT:
+  case TargetOpcode::G_USHLSAT:
+    return includesPoison(Kind) &&
+           !shiftAmountKnownInRange(RegDef->getOperand(2).getReg(), MRI);
----------------
arsenm wrote:

Test doesn't look comprehensive, this for example doesn't seem covered 

https://github.com/llvm/llvm-project/pull/93239