[PATCH] D117831: [AVR] Remove regalloc workaround for LDDWRdPtrQ

[Ayke via Phabricator via llvm-commits]

aykevl created this revision.
aykevl added reviewers: dylanmckay, benshi001.
Herald added subscribers: Jim, JDevlieghere, hiraditya.
aykevl requested review of this revision.
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Background: https://github.com/avr-rust/rust-legacy-fork/issues/126

In short, this workaround was introduced to fix a "ran out of registers
during regalloc" issue. The root cause has since been fixed in
https://reviews.llvm.org/D54218 so this workaround can be removed.

There is one test that changes a little bit, removing a single
instruction. I also compiled compiler-rt before and after this patch but
didn't see a difference. So presumably the impact is very low. Still,
it's nice to be able to remove such a workaround.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117831

Files:
  llvm/lib/Target/AVR/AVRInstrInfo.td
  llvm/lib/Target/AVR/AVRRegisterInfo.td
  llvm/test/CodeGen/AVR/lpmx.ll


Index: llvm/test/CodeGen/AVR/lpmx.ll
===================================================================
--- llvm/test/CodeGen/AVR/lpmx.ll
+++ llvm/test/CodeGen/AVR/lpmx.ll
@@ -22,13 +22,12 @@
 ; CHECK-O0-NEXT:    out 61, r28
 ; CHECK-O0-NEXT:    std Y+1, r24
 ; CHECK-O0-NEXT:    std Y+2, r25
-; CHECK-O0-NEXT:    ldd r24, Y+1
-; CHECK-O0-NEXT:    ldd r25, Y+2
-; CHECK-O0-NEXT:    lsl r24
-; CHECK-O0-NEXT:    rol r25
-; CHECK-O0-NEXT:    subi r24, -lo8(arr0)
-; CHECK-O0-NEXT:    sbci r25, -hi8(arr0)
-; CHECK-O0-NEXT:    movw r30, r24
+; CHECK-O0-NEXT:    ldd r30, Y+1
+; CHECK-O0-NEXT:    ldd r31, Y+2
+; CHECK-O0-NEXT:    lsl r30
+; CHECK-O0-NEXT:    rol r31
+; CHECK-O0-NEXT:    subi r30, -lo8(arr0)
+; CHECK-O0-NEXT:    sbci r31, -hi8(arr0)
 ; CHECK-O0-NEXT:    lpm r24, Z+
 ; CHECK-O0-NEXT:    lpm r25, Z
 ; CHECK-O0-NEXT:    adiw r28, 2
@@ -95,11 +94,10 @@
 ; CHECK-O0-NEXT:    out 61, r28
 ; CHECK-O0-NEXT:    std Y+1, r24
 ; CHECK-O0-NEXT:    std Y+2, r25
-; CHECK-O0-NEXT:    ldd r24, Y+1
-; CHECK-O0-NEXT:    ldd r25, Y+2
-; CHECK-O0-NEXT:    subi r24, -lo8(arr1)
-; CHECK-O0-NEXT:    sbci r25, -hi8(arr1)
-; CHECK-O0-NEXT:    movw r30, r24
+; CHECK-O0-NEXT:    ldd r30, Y+1
+; CHECK-O0-NEXT:    ldd r31, Y+2
+; CHECK-O0-NEXT:    subi r30, -lo8(arr1)
+; CHECK-O0-NEXT:    sbci r31, -hi8(arr1)
 ; CHECK-O0-NEXT:    lpm r24, Z
 ; CHECK-O0-NEXT:    adiw r28, 2
 ; CHECK-O0-NEXT:    in r0, 63
Index: llvm/lib/Target/AVR/AVRRegisterInfo.td
===================================================================
--- llvm/lib/Target/AVR/AVRRegisterInfo.td
+++ llvm/lib/Target/AVR/AVRRegisterInfo.td
@@ -186,26 +186,6 @@
 // allow r30 or r31 as output operands.
 def DREGSLPM : RegisterClass<"AVR", [i16], 8, (sub DREGS, R31R30)>;
 
-// The 16-bit DREGS register class, excluding the Z pointer register.
-//
-// This is used by instructions which cause high pointer register
-// contention which leads to an assertion in the register allocator.
-//
-// There is no technical reason why instructions that use this class
-// cannot use Z; it's simply a workaround a regalloc bug.
-//
-// More information can be found in PR39553.
-def DREGS_WITHOUT_YZ_WORKAROUND
-    : RegisterClass<"AVR", [i16], 8,
-                    (
-                        // Return value and arguments.
-                        add R25R24, R19R18, R21R20, R23R22,
-                        // Scratch registers.
-                        R27R26,
-                        // Callee saved registers.
-                        R17R16, R15R14, R13R12, R11R10, R9R8, R7R6, R5R4, R3R2,
-                        R1R0)>;
-
 // 16-bit register class for immediate instructions.
 def DLDREGS : RegisterClass<"AVR", [i16], 8,
                             (
Index: llvm/lib/Target/AVR/AVRInstrInfo.td
===================================================================
--- llvm/lib/Target/AVR/AVRInstrInfo.td
+++ llvm/lib/Target/AVR/AVRInstrInfo.td
@@ -1394,7 +1394,7 @@
   // ldd Rd,   P+q
   // ldd Rd+1, P+q+1
   let Constraints = "@earlyclobber $dst" in def LDDWRdPtrQ
-      : Pseudo<(outs DREGS_WITHOUT_YZ_WORKAROUND
+      : Pseudo<(outs DREGS
                 : $dst),
                (ins memri
                 : $memri),


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