[GISel] Add LookThroughInstrs for getIConstantVRegVal and getIConstan… (#68327)

…tVRegSExtVal

The implementation of these methods uses
getIConstantVRegValWithLookThrough with LookThroughInstrs argument set
to false. By adding the optional argument to getIConstantVRegVal and
getIConstantVRegSExtVal we can take advantage of the already built look
through functionality.

Author: michaelmaitland

llvm/include/llvm/CodeGen/GlobalISel/Utils.h

@@ -171,11 +171,13 @@ void reportGISelWarning(MachineFunction &MF, const TargetPassConfig &TPC,
 
 /// If \p VReg is defined by a G_CONSTANT, return the corresponding value.
 std::optional<APInt> getIConstantVRegVal(Register VReg,
-                                         const MachineRegisterInfo &MRI);
+                                         const MachineRegisterInfo &MRI,
+                                         bool LookThroughInstrs = false);
 
 /// If \p VReg is defined by a G_CONSTANT fits in int64_t returns it.
 std::optional<int64_t> getIConstantVRegSExtVal(Register VReg,
-                                               const MachineRegisterInfo &MRI);
+                                               const MachineRegisterInfo &MRI,
+                                               bool LookThroughInstrs = false);
 
 /// Simple struct used to hold a constant integer value and a virtual
 /// register.

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -290,9 +290,10 @@ void llvm::reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
 }
 
 std::optional<APInt> llvm::getIConstantVRegVal(Register VReg,
-                                               const MachineRegisterInfo &MRI) {
-  std::optional<ValueAndVReg> ValAndVReg = getIConstantVRegValWithLookThrough(
-      VReg, MRI, /*LookThroughInstrs*/ false);
+                                               const MachineRegisterInfo &MRI,
+                                               bool LookThroughInstrs) {
+  std::optional<ValueAndVReg> ValAndVReg =
+      getIConstantVRegValWithLookThrough(VReg, MRI, LookThroughInstrs);
   assert((!ValAndVReg || ValAndVReg->VReg == VReg) &&
          "Value found while looking through instrs");
   if (!ValAndVReg)
@@ -301,8 +302,9 @@ std::optional<APInt> llvm::getIConstantVRegVal(Register VReg,
 }
 
 std::optional<int64_t>
-llvm::getIConstantVRegSExtVal(Register VReg, const MachineRegisterInfo &MRI) {
-  std::optional<APInt> Val = getIConstantVRegVal(VReg, MRI);
+llvm::getIConstantVRegSExtVal(Register VReg, const MachineRegisterInfo &MRI,
+                              bool LookThroughInstrs) {
+  std::optional<APInt> Val = getIConstantVRegVal(VReg, MRI, LookThroughInstrs);
   if (Val && Val->getBitWidth() <= 64)
     return Val->getSExtValue();
   return std::nullopt;