[AMDGPU] Fix source location for assembler warnings (#156621)

Call MCInst::setLoc earlier so it is available for warnings generated
during MatchInstructionImpl.

Author: jayfoad

llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp

@@ -5832,6 +5832,7 @@ bool AMDGPUAsmParser::matchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
                                               uint64_t &ErrorInfo,
                                               bool MatchingInlineAsm) {
   MCInst Inst;
+  Inst.setLoc(IDLoc);
   unsigned Result = Match_Success;
   for (auto Variant : getMatchedVariants()) {
     uint64_t EI;
@@ -5855,7 +5856,6 @@ bool AMDGPUAsmParser::matchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
     if (!validateInstruction(Inst, IDLoc, Operands)) {
       return true;
     }
-    Inst.setLoc(IDLoc);
     Out.emitInstruction(Inst, getSTI());
     return false;
   }

llvm/test/MC/AMDGPU/warnings.s

@@ -0,0 +1,5 @@
+// NOTE: Assertions have been autogenerated by utils/update_mc_test_checks.py UTC_ARGS: --version 5
+// RUN: llvm-mc -triple=amdgcn -mcpu=gfx900 -filetype=null %s 2>&1 | FileCheck %s
+
+v_floor_f64 v[0:1], 1.23456
+// CHECK: :[[@LINE-1]]:1: warning: Can't encode literal as exact 64-bit floating-point operand. Low 32-bits will be set to zero