[llvm-dev] sinking in LICM

[via llvm-dev]

Hi,

In the IR below, %tmp.7 and %tmp.8 are not used in loop, so we can sink 
them in exit blocks. However, LICM do not handle this case because of 
the check in isNotUsedInLoop() which returns false when a PHI node use 
is hooked from a block inside the loop. I'm not sure if we really need 
to have this check even when the PHI is outside the loop?

define i32 @test7(i32 %N, i32 %N2, i1 %C) {
Entry:
         br label %Loop
Loop:
         %N_addr.0.pn = phi i32 [ %dec, %ContLoop ], [ %N, %Entry ]
         %tmp.6 = mul i32 %N, %N_addr.0.pn
         %tmp.7 = sub i32 %tmp.6, %N
         %tmp.8 = sub i32 %tmp.6, %N2
         %dec = add i32 %N_addr.0.pn, -1
         br i1 %C, label %ContLoop, label %Out12

ContLoop:
         %tmp.1 = icmp ne i32 %N_addr.0.pn, 1
         br i1 %tmp.1, label %Loop, label %Out12

Out12:
   %tmp.7.8.lcssa1 = phi i32 [%tmp.8, %ContLoop], [%tmp.7, %Loop]
   ret i32 %tmp.7.8.lcssa1
}

Is there any problem I'm missing if we convert the above IR to the IR 
below :

define i32 @test7(i32 %N, i32 %N2, i1 %C) {
Entry:
   br label %Loop

Loop:
   %N_addr.0.pn = phi i32 [ %dec, %ContLoop ], [ %N, %Entry ]
   %dec = add i32 %N_addr.0.pn, -1
   br i1 %C, label %ContLoop, label %Out01

ContLoop:
   %tmp.1 = icmp ne i32 %N_addr.0.pn, 1
   br i1 %tmp.1, label %Loop, label %Out02

Out01:
   %N_addr.0.pn.lcssa2 = phi i32 [ %N_addr.0.pn, %Loop ]
   %tmp.6.le1 = mul i32 %N, %N_addr.0.pn.lcssa2
   %tmp.8.new = sub i32 %tmp.6.le1, %N2
   br label %Out12

Out02:
   %N_addr.0.pn.lcssa = phi i32 [ %N_addr.0.pn, %ContLoop ]
   %tmp.6.le = mul i32 %N, %N_addr.0.pn.lcssa
   %tmp.7.new = sub i32 %tmp.6.le, %N
   br label %Out12

Out12:
   %tmp.7.8.ret = phi i32 [ %tmp.8.new, %Out01 ], [ %tmp.7.new, %Out02 ]
   ret i32 %tmp.7.8.ret
}

Thanks,
Jun


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