[llvm] [llvm] Win x64 Unwind V2 1/n: Mark beginning and end of epilogs (PR #110024)

[Eli Friedman via llvm-commits]

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@@ -178,12 +188,16 @@ define i32 @loopInfoSaveOutsideLoop2(i32 %cond, i32 %N) #0 {
 ; DISABLE-NEXT:    nop
 ; DISABLE-NEXT:    #NO_APP
 ; DISABLE-NEXT:    shll $3, %eax
-; DISABLE-NEXT:    jmp .LBB1_5
-; DISABLE-NEXT:  .LBB1_4: # %if.else
+; DISABLE-NEXT:    .seh_startepilogue
+; DISABLE-NEXT:    popq %rbx
+; DISABLE-NEXT:    .seh_endepilogue
+; DISABLE-NEXT:    retq
+; DISABLE-NEXT:  .LBB1_5: # %if.else
 ; DISABLE-NEXT:    addl %edx, %edx
 ; DISABLE-NEXT:    movl %edx, %eax
-; DISABLE-NEXT:  .LBB1_5: # %if.end
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efriedma-quic wrote:

Adding an SEH directive shouldn't affect block layout/merging this way.  Can we fix the heuristic here so it isn't sensitive to this?

https://github.com/llvm/llvm-project/pull/110024