[DebugInfo] Make describeLoadedValue() reg aware

Currently the describeLoadedValue() hook is assumed to describe the
value of the instruction's first explicit define. The hook will not be
called for instructions with more than one explicit define.

This commit adds a register parameter to the describeLoadedValue() hook,
and invokes the hook for all registers in the worklist.

This will allow us to for example describe instructions which produce
more than two parameters' values; e.g. Hexagon's various combine
instructions.

This also fixes a case in our downstream target where we may pass
smaller parameters in the high part of a register. If such a parameter's
value is produced by a larger copy instruction, we can't describe the
call site value using the super-register, and we instead need to know
which sub-register that should be used.

This also allows us to handle cases like this:

  $ebx = [...]
  $rdi = MOVSX64rr32 $ebx
  $esi = MOV32rr $edi
  CALL64pcrel32 @call

The hook will first be invoked for the MOV32rr instruction, which will
say that @call's second parameter (passed in $esi) is described by $edi.
As $edi is not preserved it will be added to the worklist. When we get
to the MOVSX64rr32 instruction, we need to describe two values; the
sign-extended value of $ebx -> $rdi for the first parameter, and $ebx ->
$edi for the second parameter, which is now possible.

This commit modifies the dbgcall-site-lea-interpretation.mir test case.
In the test case, the values of some 32-bit parameters were produced
with LEA64r. Perhaps we can in general cases handle such by emitting
expressions that AND out the lower 32-bits, but I have not been able to
land in a case where a LEA64r is used for a 32-bit parameter instead of
LEA64_32 from C code.

I have not found a case where it would be useful to describe parameters
using implicit defines, so in this patch the hook is still only invoked
for explicit defines of forwarding registers.

1 files changed, 26 insertions, 33 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 0aa4ae3958e..89a0e350f8f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -595,7 +595,6 @@ static void collectCallSiteParameters(const MachineInstr *CallMI,
               Implicit.push_back(FwdReg);
             else
               Explicit.push_back(FwdReg);
-            break;
           }
         }
       }
@@ -640,39 +639,33 @@ static void collectCallSiteParameters(const MachineInstr *CallMI,
     for (auto Reg : concat<unsigned>(ExplicitFwdRegDefs, ImplicitFwdRegDefs))
       ForwardedRegWorklist.erase(Reg);
 
-    // The describeLoadedValue() hook currently does not have any information
-    // about which register it should describe in case of multiple defines, so
-    // for now we only handle instructions where a forwarded register is (at
-    // least partially) defined by the instruction's single explicit define.
-    if (I->getNumExplicitDefs() != 1 || ExplicitFwdRegDefs.empty())
-      continue;
-    unsigned ParamFwdReg = ExplicitFwdRegDefs[0];
-
-    if (auto ParamValue = TII->describeLoadedValue(*I)) {
-      if (ParamValue->first.isImm()) {
-        int64_t Val = ParamValue->first.getImm();
-        DbgValueLoc DbgLocVal(ParamValue->second, Val);
-        finishCallSiteParam(DbgLocVal, ParamFwdReg);
-      } else if (ParamValue->first.isReg()) {
-        Register RegLoc = ParamValue->first.getReg();
-       // TODO: For now, there is no use of describing the value loaded into the
-       //       register that is also the source registers (e.g. $r0 = add $r0, x).
-       if (ParamFwdReg == RegLoc)
-         continue;
-
-        unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
-        Register FP = TRI->getFrameRegister(*MF);
-        bool IsSPorFP = (RegLoc == SP) || (RegLoc == FP);
-        if (TRI->isCalleeSavedPhysReg(RegLoc, *MF) || IsSPorFP) {
-          DbgValueLoc DbgLocVal(ParamValue->second,
-                                MachineLocation(RegLoc,
-                                                /*IsIndirect=*/IsSPorFP));
+    for (auto ParamFwdReg : ExplicitFwdRegDefs) {
+      if (auto ParamValue = TII->describeLoadedValue(*I, ParamFwdReg)) {
+        if (ParamValue->first.isImm()) {
+          int64_t Val = ParamValue->first.getImm();
+          DbgValueLoc DbgLocVal(ParamValue->second, Val);
           finishCallSiteParam(DbgLocVal, ParamFwdReg);
-        // TODO: Add support for entry value plus an expression.
-        } else if (ShouldTryEmitEntryVals &&
-                   ParamValue->second->getNumElements() == 0) {
-          ForwardedRegWorklist.insert(RegLoc);
-          RegsForEntryValues[RegLoc] = ParamFwdReg;
+        } else if (ParamValue->first.isReg()) {
+          Register RegLoc = ParamValue->first.getReg();
+          // TODO: For now, there is no use of describing the value loaded into the
+          //       register that is also the source registers (e.g. $r0 = add $r0, x).
+          if (ParamFwdReg == RegLoc)
+            continue;
+
+          unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
+          Register FP = TRI->getFrameRegister(*MF);
+          bool IsSPorFP = (RegLoc == SP) || (RegLoc == FP);
+          if (TRI->isCalleeSavedPhysReg(RegLoc, *MF) || IsSPorFP) {
+            DbgValueLoc DbgLocVal(ParamValue->second,
+                                  MachineLocation(RegLoc,
+                                                  /*IsIndirect=*/IsSPorFP));
+            finishCallSiteParam(DbgLocVal, ParamFwdReg);
+          // TODO: Add support for entry value plus an expression.
+          } else if (ShouldTryEmitEntryVals &&
+                     ParamValue->second->getNumElements() == 0) {
+            ForwardedRegWorklist.insert(RegLoc);
+            RegsForEntryValues[RegLoc] = ParamFwdReg;
+          }
         }
       }
     }