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

This reverts commit 28ae42e.

The assert in getIConstantVRegVal was not updated for this change.
The ValAndVReg->VReg == VReg check fails if any look through happens.

RISC-V was the only target using the lookthrough functionality, but I'm
not sure it was needed so I'm removing that too.

Author: topperc

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

@@ -171,13 +171,11 @@ 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,
-                                         bool LookThroughInstrs = false);
+                                         const MachineRegisterInfo &MRI);
 
 /// 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,
-                                               bool LookThroughInstrs = false);
+                                               const MachineRegisterInfo &MRI);
 
 /// Simple struct used to hold a constant integer value and a virtual
 /// register.

llvm/lib/CodeGen/GlobalISel/Utils.cpp

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

llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp

@@ -763,7 +763,7 @@ static void getICMPOperandsForBranch(MachineInstr &MI, MachineIRBuilder &MIB,
   RHS = MI.getOperand(3).getReg();
 
   // Adjust comparisons to use comparison with 0 if possible.
-  if (auto Constant = getIConstantVRegSExtVal(RHS, MRI, true)) {
+  if (auto Constant = getIConstantVRegSExtVal(RHS, MRI)) {
     switch (ICMPCC) {
     case CmpInst::Predicate::ICMP_SGT:
       // Convert X > -1 to X >= 0