<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/61266>61266</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
InstCombine drops debug value after simplifying to boolean
</td>
</tr>
<tr>
<th>Labels</th>
<td>
debuginfo,
llvm:instcombine
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
jryans
</td>
</tr>
</table>
<pre>
The `InstCombine` pass simplifies `health_started` to a boolean value, but in
doing so, it loses the debug value info for `health_started` at the point of the
`cleanup` label.
## Versions
* Clang: version 17.0.0 (https://github.com/llvm/llvm-project.git 7de0804ea3290e5e43ce38567b4056a34ccad551)
* LLDB: version 17.0.0git (git@github.com:llvm/llvm-project.git revision c820e60844ee1e5f084dd7761576bd0bd4927264)
## Compiler Explorer
* [Optimisation pipeline view using x86-64 Clang trunk (may change over time)](https://godbolt.org/z/3q1417xj6)
## Program source
```c
extern int result;
extern int bob(void);
int d() {
int health_started = 0;
if (bob())
goto cleanup;
health_started = 1;
cleanup:
if (health_started)
return ++result;
return 0;
}
```
## Debug info view
```
$ clang -fno-discard-value-names -fno-inline -g -O1 -c -o example-O1.o
$ llvm-dwarfdump -n health_started example-O1.o
0x0000004b: DW_TAG_variable
DW_AT_location (0x00000000:
[0x0000000000000004, 0x000000000000000f): DW_OP_consts +0, DW_OP_stack_value)
DW_AT_name ("health_started")
DW_AT_decl_line (5)
DW_AT_type (0x00000082 "int")
$ llvm-dwarfdump --debug-line example-O1.o
Address Line Column File ISA Discriminator Flags
------------------ ------ ------ ------ --- ------------- -------------
0x0000000000000000 4 0 1 0 0 is_stmt
0x0000000000000004 6 7 1 0 0 is_stmt prologue_end
0x000000000000000f 10 7 1 0 0 is_stmt
0x0000000000000011 13 1 1 0 0 is_stmt
0x0000000000000013 11 12 1 0 0 is_stmt
0x0000000000000021 13 1 1 0 0 is_stmt
0x0000000000000023 13 1 1 0 0 is_stmt end_sequence
```
The variable `health_started` has the location range `[0x04, 0x0f)`. The
conditional `if (health_started)` is on source line 10 / address `0x0f`. The
value should remain visible at least for the conditional (where it is used), but
currently it stops just before that.
## IR before `InstCombine`
```llvm
define dso_local i32 @d() local_unnamed_addr {
entry:
call void @llvm.dbg.value(metadata i32 0, "health_started", metadata !DIExpression())
%call = call i32 @bob()
%tobool = icmp ne i32 %call, 0
br i1 %tobool, label %cleanup, label %if.end
if.end: ; preds = %entry
call void @llvm.dbg.value(metadata i32 1, "health_started", metadata !DIExpression())
br label %cleanup
cleanup: ; preds = %entry, %if.end
%health_started.0 = phi i32 [ 0, %entry ], [ 1, %if.end ]
call void @llvm.dbg.value(metadata i32 %health_started.0, "health_started", metadata !DIExpression())
call void @llvm.dbg.label(metadata !16)
%tobool1 = icmp ne i32 %health_started.0, 0
br i1 %tobool1, label %if.then2, label %if.end3
if.then2: ; preds = %cleanup
%0 = load i32, ptr @result, align 4
%inc = add nsw i32 %0, 1
store i32 %inc, ptr @result, align 4
br label %cleanup4
if.end3: ; preds = %cleanup
br label %cleanup4
cleanup4: ; preds = %if.end3, %if.then2
%retval.0 = phi i32 [ %inc, %if.then2 ], [ 0, %if.end3 ]
ret i32 %retval.0
}
```
## IR after `InstCombine`
```llvm
define dso_local i32 @d() local_unnamed_addr {
entry:
call void @llvm.dbg.value(metadata i32 0, "health_started", metadata !DIExpression())
%call = call i32 @bob()
%tobool.not.not = icmp eq i32 %call, 0
br i1 %tobool.not.not, label %if.end, label %cleanup
if.end: ; preds = %entry
call void @llvm.dbg.value(metadata i32 1, "health_started", metadata !DIExpression())
br label %cleanup
cleanup: ; preds = %entry, %if.end
call void @llvm.dbg.value(metadata i32 poison, "health_started", metadata !DIExpression())
call void @llvm.dbg.label(metadata !16)
br i1 %tobool.not.not, label %if.then2, label %if.end3
if.then2: ; preds = %cleanup
%0 = load i32, ptr @result, align 4
%inc = add nsw i32 %0, 1
store i32 %inc, ptr @result, align 4
br label %cleanup4
if.end3: ; preds = %cleanup
br label %cleanup4
cleanup4: ; preds = %if.end3, %if.then2
%retval.0 = phi i32 [ %inc, %if.then2 ], [ 0, %if.end3 ]
ret i32 %retval.0
}
```
## IR diff before and after `InstCombine`
```diff
@@ -2,19 +2,17 @@
entry:
call void @llvm.dbg.value(metadata i32 0, "health_started", metadata !DIExpression())
%call = call i32 @bob()
- %tobool = icmp ne i32 %call, 0
- br i1 %tobool, label %cleanup, label %if.end
+ %tobool.not.not = icmp eq i32 %call, 0
+ br i1 %tobool.not.not, label %if.end, label %cleanup
if.end: ; preds = %entry
call void @llvm.dbg.value(metadata i32 1, "health_started", metadata !DIExpression())
br label %cleanup
cleanup: ; preds = %entry, %if.end
- %health_started.0 = phi i32 [ 0, %entry ], [ 1, %if.end ]
- call void @llvm.dbg.value(metadata i32 %health_started.0, "health_started", metadata !DIExpression())
+ call void @llvm.dbg.value(metadata i32 poison, "health_started", metadata !DIExpression())
call void @llvm.dbg.label(metadata !16)
- %tobool1 = icmp ne i32 %health_started.0, 0
- br i1 %tobool1, label %if.then2, label %if.end3
+ br i1 %tobool.not.not, label %if.then2, label %if.end3
if.then2: ; preds = %cleanup
%0 = load i32, ptr @result, align 4
```
</pre>
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