[RISCV] Use two ADDIs to do some stack pointer adjustments.

If the adjustment doesn't fit in 12 bits, try to break it into two 12 bit values before falling back to movImm+add/sub. This is based on a similar idea from isel. Reviewed By: luismarques, reames Differential Revision: https://reviews.llvm.org/D126392
llvm · May 31, 2022 · 1b2de79 · 1b2de79
1 parent 9d1b260
commit 1b2de79
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Showing 4 changed files with 45 additions and 29 deletions.
diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
@@ -303,21 +303,43 @@ void RISCVFrameLowering::adjustReg(MachineBasicBlock &MBB,
         .addReg(SrcReg)
         .addImm(Val)
         .setMIFlag(Flag);
-  } else {
-    unsigned Opc = RISCV::ADD;
-    bool IsSub = Val < 0;
-    if (IsSub) {
-      Val = -Val;
-      Opc = RISCV::SUB;
-    }
+    return;
+  }
 
-    Register ScratchReg = MRI.createVirtualRegister(&RISCV::GPRRegClass);
-    TII->movImm(MBB, MBBI, DL, ScratchReg, Val, Flag);
-    BuildMI(MBB, MBBI, DL, TII->get(Opc), DestReg)
+  // Try to split the offset across two ADDIs. We need to keep the stack pointer
+  // aligned after each ADDI. We need to determine the maximum value we can put
+  // in each ADDI. In the negative direction, we can use -2048 which is always
+  // sufficiently aligned. In the positive direction, we need to find the
+  // largest 12-bit immediate that is aligned. Exclude -4096 since it can be
+  // created with LUI.
+  assert(getStackAlign().value() < 2048 && "Stack alignment too large");
+  int64_t MaxPosAdjStep = 2048 - getStackAlign().value();
+  if (Val > -4096 && Val <= (2 * MaxPosAdjStep)) {
+    int64_t FirstAdj = Val < 0 ? -2048 : MaxPosAdjStep;
+    Val -= FirstAdj;
+    BuildMI(MBB, MBBI, DL, TII->get(RISCV::ADDI), DestReg)
         .addReg(SrcReg)
-        .addReg(ScratchReg, RegState::Kill)
+        .addImm(FirstAdj)
+        .setMIFlag(Flag);
+    BuildMI(MBB, MBBI, DL, TII->get(RISCV::ADDI), DestReg)
+        .addReg(DestReg, RegState::Kill)
+        .addImm(Val)
         .setMIFlag(Flag);
+    return;
   }
+
+  unsigned Opc = RISCV::ADD;
+  if (Val < 0) {
+    Val = -Val;
+    Opc = RISCV::SUB;
+  }
+
+  Register ScratchReg = MRI.createVirtualRegister(&RISCV::GPRRegClass);
+  TII->movImm(MBB, MBBI, DL, ScratchReg, Val, Flag);
+  BuildMI(MBB, MBBI, DL, TII->get(Opc), DestReg)
+      .addReg(SrcReg)
+      .addReg(ScratchReg, RegState::Kill)
+      .setMIFlag(Flag);
 }
 
 // Returns the register used to hold the frame pointer.

diff --git a/llvm/test/CodeGen/RISCV/rvv/emergency-slot.mir b/llvm/test/CodeGen/RISCV/rvv/emergency-slot.mir
@@ -153,9 +153,8 @@ body:             |
   ; CHECK-NEXT:   PseudoBR %bb.2
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.2:
-  ; CHECK-NEXT:   $x10 = frame-destroy LUI 1
-  ; CHECK-NEXT:   $x10 = frame-destroy ADDIW killed $x10, -1792
-  ; CHECK-NEXT:   $x2 = frame-destroy SUB $x8, killed $x10
+  ; CHECK-NEXT:   $x2 = frame-destroy ADDI $x8, -2048
+  ; CHECK-NEXT:   $x2 = frame-destroy ADDI killed $x2, -256
   ; CHECK-NEXT:   $x2 = frame-destroy ADDI $x2, 272
   ; CHECK-NEXT:   $x1 = LD $x2, 2024 :: (load (s64) from %stack.3)
   ; CHECK-NEXT:   $x8 = LD $x2, 2016 :: (load (s64) from %stack.4)

diff --git a/llvm/test/CodeGen/RISCV/rvv/large-rvv-stack-size.mir b/llvm/test/CodeGen/RISCV/rvv/large-rvv-stack-size.mir
@@ -32,9 +32,8 @@
   ; CHECK-NEXT:    vs1r.v v25, (a0) # Unknown-size Folded Spill
   ; CHECK-NEXT:    ld a0, 8(sp)
   ; CHECK-NEXT:    call spillslot@plt
-  ; CHECK-NEXT:    lui a0, 1
-  ; CHECK-NEXT:    addiw a0, a0, -1792
-  ; CHECK-NEXT:    sub sp, s0, a0
+  ; CHECK-NEXT:    addi sp, s0, -2048
+  ; CHECK-NEXT:    addi sp, sp, -256
   ; CHECK-NEXT:    addi sp, sp, 272
   ; CHECK-NEXT:    ld ra, 2024(sp) # 8-byte Folded Reload
   ; CHECK-NEXT:    ld s0, 2016(sp) # 8-byte Folded Reload

diff --git a/llvm/test/CodeGen/RISCV/stack-realignment.ll b/llvm/test/CodeGen/RISCV/stack-realignment.ll
@@ -453,19 +453,17 @@ define void @caller2048() {
 ; RV32I-NEXT:    .cfi_offset s0, -8
 ; RV32I-NEXT:    addi s0, sp, 2032
 ; RV32I-NEXT:    .cfi_def_cfa s0, 0
-; RV32I-NEXT:    lui a0, 1
-; RV32I-NEXT:    addi a0, a0, -2032
-; RV32I-NEXT:    sub sp, sp, a0
+; RV32I-NEXT:    addi sp, sp, -2048
+; RV32I-NEXT:    addi sp, sp, -16
 ; RV32I-NEXT:    andi sp, sp, -2048
 ; RV32I-NEXT:    lui a0, 1
 ; RV32I-NEXT:    addi a0, a0, -2048
 ; RV32I-NEXT:    add a0, sp, a0
 ; RV32I-NEXT:    call callee@plt
 ; RV32I-NEXT:    lui a0, 1
 ; RV32I-NEXT:    sub sp, s0, a0
-; RV32I-NEXT:    lui a0, 1
-; RV32I-NEXT:    addi a0, a0, -2032
-; RV32I-NEXT:    add sp, sp, a0
+; RV32I-NEXT:    addi sp, sp, 2032
+; RV32I-NEXT:    addi sp, sp, 32
 ; RV32I-NEXT:    lw ra, 2028(sp) # 4-byte Folded Reload
 ; RV32I-NEXT:    lw s0, 2024(sp) # 4-byte Folded Reload
 ; RV32I-NEXT:    addi sp, sp, 2032
@@ -481,19 +479,17 @@ define void @caller2048() {
 ; RV64I-NEXT:    .cfi_offset s0, -16
 ; RV64I-NEXT:    addi s0, sp, 2032
 ; RV64I-NEXT:    .cfi_def_cfa s0, 0
-; RV64I-NEXT:    lui a0, 1
-; RV64I-NEXT:    addiw a0, a0, -2032
-; RV64I-NEXT:    sub sp, sp, a0
+; RV64I-NEXT:    addi sp, sp, -2048
+; RV64I-NEXT:    addi sp, sp, -16
 ; RV64I-NEXT:    andi sp, sp, -2048
 ; RV64I-NEXT:    lui a0, 1
 ; RV64I-NEXT:    addiw a0, a0, -2048
 ; RV64I-NEXT:    add a0, sp, a0
 ; RV64I-NEXT:    call callee@plt
 ; RV64I-NEXT:    lui a0, 1
 ; RV64I-NEXT:    sub sp, s0, a0
-; RV64I-NEXT:    lui a0, 1
-; RV64I-NEXT:    addiw a0, a0, -2032
-; RV64I-NEXT:    add sp, sp, a0
+; RV64I-NEXT:    addi sp, sp, 2032
+; RV64I-NEXT:    addi sp, sp, 32
 ; RV64I-NEXT:    ld ra, 2024(sp) # 8-byte Folded Reload
 ; RV64I-NEXT:    ld s0, 2016(sp) # 8-byte Folded Reload
 ; RV64I-NEXT:    addi sp, sp, 2032