[PATCH] Add CHECK-LABEL directive to FileCheck to allow more accurate error messages and error recovery

[Stephen Lin]

Hi,

Can anyone review this patch? It adds a new directive type called
"CHECK-LABEL" to FileCheck...

If present in a match file, FileCheck will use these directives to
split the input into blocks that are independently processed, ensuring
that a CHECK does not inadvertently match a line in a different block
(which can lead to a misleading/useless error message when the error
is eventually caught). Also, FileCheck can now recover from errors
within blocks by continuing to the next block.

As an example, I purposely introduced the a switch fall-through bug in
the last patch I submitted to llvm-commits ("Allow FMAs in safe math
mode in some cases when one operand of the fmul is either exactly 0.0
or exactly 1.0")...

Bug diff:

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 0290afc..239b119 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5791,7 +5791,7 @@ static bool isExactlyZeroOrOne(const
TargetLowering &TLI, const SDValue &Op) {
           continue;
         }
       }
-      break;
+//      break;
     case ISD::FADD:
       if (ConstantFPSDNode *V0CFP =
             dyn_cast<ConstantFPSDNode>(V->getOperand(0))) {

The single error message without CHECK-LABEL is:

; CHECK-SAFE: test_add_8
              ^
<stdin>:125:2: note: scanning from here
 .cfi_endproc
 ^
<stdin>:127:10: note: possible intended match here
 .globl _test_add_10
         ^

The error messages with CHECK-LABEL are:

; CHECK-SAFE: vmulsd
              ^
<stdin>:87:2: note: scanning from here
 .align 4, 0x90
 ^
<stdin>:95:2: note: possible intended match here
 vsubsd %xmm0, %xmm3, %xmm0
 ^
fp-contract.ll:118:15: error: expected string not found in input
; CHECK-SAFE: vmulsd
              ^
<stdin>:102:2: note: scanning from here
 .align 4, 0x90
 ^
<stdin>:109:2: note: possible intended match here
 vsubsd %xmm2, %xmm3, %xmm2
 ^
fp-contract.ll:288:15: error: expected string not found in input
; CHECK-SAFE: vmulsd
              ^
<stdin>:258:2: note: scanning from here
 .align 4, 0x90
 ^
<stdin>:266:2: note: possible intended match here
 vsubsd %xmm0, %xmm3, %xmm0
 ^

The three error messages in the CHECK-LABEL case exactly pinpoint the
source lines of the actual problem in three separate blocks; the
single error message given without CHECK-LABEL is (imho) much less
useful.

(In this case, the non-CHECK-LABEL version happens to error on the on
a label line, so the user could presume that the error happened in the
block immediately before test_add_8, which is correct, but in general
this might not be true; the only thing that can be concluded is that
the error happened sometime before test_add_8.)

Please let me know if you have any feedback.

Stephen

---------- Forwarded message ----------
From: Stephen Lin <swlin at apple.com>
Date: Mon, Jun 10, 2013 at 4:21 PM
Subject: [PATCH] Add CHECK-LABEL directive to FileCheck to allow more
accurate error messages and error recovery
To: llvm-commits at cs.uiuc.edu


Actually, I went ahead and renamed it CHECK-LABEL and rebased, since I
think it’s better :)
-Stephen
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