[Local] replaceAllDbgUsesWith: Update debug values before RAUW

The replaceAllDbgUsesWith utility helps passes preserve debug info when
replacing one value with another.

This improves upon the existing insertReplacementDbgValues API by:

- Updating debug intrinsics in-place, while preventing use-before-def of
  the replacement value.
- Falling back to salvageDebugInfo when a replacement can't be made.
- Moving the responsibiliy for rewriting llvm.dbg.* DIExpressions into
  common utility code.

Along with the API change, this teaches replaceAllDbgUsesWith how to
create DIExpressions for three basic integer and pointer conversions:

- The no-op conversion. Applies when the values have the same width, or
  have bit-for-bit compatible pointer representations.
- Truncation. Applies when the new value is wider than the old one.
- Zero/sign extension. Applies when the new value is narrower than the
  old one.

Testing:

- check-llvm, check-clang, a stage2 `-g -O3` build of clang,
  regression/unit testing.
- This resolves a number of mis-sized dbg.value diagnostics from
  Debugify.

Differential Revision: https://reviews.llvm.org/D48676

llvm-svn: 336451

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index 043d02e3ce4..d8d1a5e8f84 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -357,6 +357,9 @@ void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
     case dwarf::DW_OP_shl:
     case dwarf::DW_OP_shr:
     case dwarf::DW_OP_shra:
+    case dwarf::DW_OP_lit0:
+    case dwarf::DW_OP_not:
+    case dwarf::DW_OP_dup:
       emitOp(Op->getOp());
       break;
     case dwarf::DW_OP_deref: