[llvm][PPC] Add missing case for 'I' asm memory operands

From https://llvm.org/docs/LangRef.html#asm-template-argument-modifiers:

I: Print the letter ‘i’ if the operand is an integer constant,
otherwise nothing. Used to print ‘addi’ vs ‘add’ instructions.

Differential Revision: https://reviews.llvm.org/D103968

(cherry picked from commit a9e4f91)

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -321,6 +321,12 @@ bool PPCAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
       O << "0, ";
       printOperand(MI, OpNo, O);
       return false;
+    case 'I':
+      // Write 'i' if an integer constant, otherwise nothing.  Used to print
+      // addi vs add, etc.
+      if (MI->getOperand(OpNo).isImm())
+        O << "i";
+      return false;
     case 'U': // Print 'u' for update form.
     case 'X': // Print 'x' for indexed form.
       // FIXME: Currently for PowerPC memory operands are always loaded

llvm/test/CodeGen/PowerPC/asm-template-I.ll

@@ -0,0 +1,19 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc64le-- | FileCheck %s
+; https://bugs.llvm.org/show_bug.cgi?id=50608
+
+define dso_local signext i32 @main(i32 signext %argc, i8** %argv) {
+; CHECK-LABEL: main:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    stw 3, -4(1)
+; CHECK-NEXT:    li 3, 0
+; CHECK-NEXT:    addi 4, 1, -4
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    .ascii "-1@0(4)"
+; CHECK-NEXT:    .byte 0
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    blr
+entry:
+  call void asm sideeffect " .asciz \22${0:n}@${1:I}$1\22 ", "n,nZr"(i32 1, i32 %argc)
+  ret i32 0
+}