David Stenberg 731658f937 [DebugInfo] Stop describing imms in TargetInstrInfo's describeLoadedValue() impl ... Summary: The default implementation of the describeLoadedValue() hook uses the MoveImm property to determine if an instruction moves an immediate. If an instruction has that property the function returns the second operand, assuming that that is the immediate value the instruction moves. As far as I can tell, the MoveImm property does not imply that the second operand is the immediate value, nor that any other operand necessarily holds the immediate value; it just means that the instruction moves some immediate value. One example where the second operand is not the immediate is SystemZ's LZER instruction, which moves a zero immediate implicitly: $f0S = LZER. That case triggered an out-of-bound assertion when getting the operand. I have added a test case for that instruction. Another example is ARM's MVN instruction, which holds the logical bitwise NOT'd value of the immediate that is moved. For the following reproducer: extern void foo(int); int main() { foo(-11); } an incorrect call site value would be emitted: $ clang --target=arm foo.c -O1 -g -Xclang -femit-debug-entry-values \ -c -o - | ./build/bin/llvm-dwarfdump - | \ grep -A2 call_site_parameter 0x00000058: DW_TAG_GNU_call_site_parameter DW_AT_location (DW_OP_reg0 R0) DW_AT_GNU_call_site_value (DW_OP_lit10) Another example is the A2_combineii instruction on Hexagon which moves two immediates to a super-register: $d0 = A2_combineii 20, 10. Perhaps these are rare exceptions, and most MoveImm instructions hold the immediate in the second operand, but in my opinion the default implementation of the hook should only describe values that it can, by some contract, guarantee are safe to describe, rather than leaving it up to the targets to override the exceptions, as that can silently result in incorrect call site values. This patch adds X86's relevant move immediate instructions to the target's hook implementation, so this commit should be a NFC for that target. We need to do the same for ARM and AArch64. Reviewers: djtodoro, NikolaPrica, aprantl, vsk Reviewed By: vsk Subscribers: kristof.beyls, hiraditya, llvm-commits Tags: #debug-info, #llvm Differential Revision: https://reviews.llvm.org/D69109		2019-10-23 11:41:29 +02:00
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call-site-lzer.mir
lit.local.cfg