AMDGPU: Disable pattern matching "x<<32-y>>32-y" to "bfe x, 0, y" (#114279)

It is not correct to lower "x<<32-y>>32-y" to "bfe x, 0, y". When y
equals to 32, the left-hand side is still x (unchanged), however, the
right-hand side will be evaluated to 0. So it is not always correct to
do such transformation.

We may be able to keep the pattern for immediate y while y is within [0,
31]. However, the immediate operands of the sub (32 - y) are easily
folded, and "(x << imm) >> imm" will be lowered to "and x,
(2^(32-imm))-1" anyway. So no bfe matching is needed.

Author: changpeng

llvm/lib/Target/AMDGPU/SIInstructions.td

@@ -3553,19 +3553,6 @@ def : AMDGPUPat <
   (V_BFE_U32_e64 $src, (i32 0), $width)
 >;
 
-// x << (bitwidth - y) >> (bitwidth - y)
-def : AMDGPUPat <
-  (DivergentBinFrag<srl> (shl_oneuse i32:$src, (sub 32, i32:$width)),
-                         (sub 32, i32:$width)),
-  (V_BFE_U32_e64 $src, (i32 0), $width)
->;
-
-def : AMDGPUPat <
-  (DivergentBinFrag<sra> (shl_oneuse i32:$src, (sub 32, i32:$width)),
-                         (sub 32, i32:$width)),
-  (V_BFE_I32_e64 $src, (i32 0), $width)
->;
-
 // SHA-256 Ma patterns
 
 // ((x & z) | (y & (x | z))) -> BFI (XOR x, y), z, y

llvm/test/CodeGen/AMDGPU/bfe-patterns.ll

@@ -17,7 +17,9 @@ define amdgpu_kernel void @v_ubfe_sub_i32(ptr addrspace(1) %out, ptr addrspace(1
 ; SI-NEXT:    buffer_load_dword v3, v[0:1], s[4:7], 0 addr64 glc
 ; SI-NEXT:    s_waitcnt vmcnt(0)
 ; SI-NEXT:    s_mov_b64 s[2:3], s[6:7]
-; SI-NEXT:    v_bfe_u32 v2, v2, 0, v3
+; SI-NEXT:    v_sub_i32_e32 v3, vcc, 32, v3
+; SI-NEXT:    v_lshlrev_b32_e32 v2, v3, v2
+; SI-NEXT:    v_lshrrev_b32_e32 v2, v3, v2
 ; SI-NEXT:    buffer_store_dword v2, v[0:1], s[0:3], 0 addr64
 ; SI-NEXT:    s_endpgm
 ;
@@ -36,7 +38,9 @@ define amdgpu_kernel void @v_ubfe_sub_i32(ptr addrspace(1) %out, ptr addrspace(1
 ; VI-NEXT:    v_mov_b32_e32 v1, s1
 ; VI-NEXT:    v_add_u32_e32 v0, vcc, s0, v2
 ; VI-NEXT:    v_addc_u32_e32 v1, vcc, 0, v1, vcc
-; VI-NEXT:    v_bfe_u32 v2, v3, 0, v4
+; VI-NEXT:    v_sub_u32_e32 v2, vcc, 32, v4
+; VI-NEXT:    v_lshlrev_b32_e32 v3, v2, v3
+; VI-NEXT:    v_lshrrev_b32_e32 v2, v2, v3
 ; VI-NEXT:    flat_store_dword v[0:1], v2
 ; VI-NEXT:    s_endpgm
   %id.x = tail call i32 @llvm.amdgcn.workitem.id.x()
@@ -215,7 +219,9 @@ define amdgpu_kernel void @v_sbfe_sub_i32(ptr addrspace(1) %out, ptr addrspace(1
 ; SI-NEXT:    buffer_load_dword v3, v[0:1], s[4:7], 0 addr64 glc
 ; SI-NEXT:    s_waitcnt vmcnt(0)
 ; SI-NEXT:    s_mov_b64 s[2:3], s[6:7]
-; SI-NEXT:    v_bfe_i32 v2, v2, 0, v3
+; SI-NEXT:    v_sub_i32_e32 v3, vcc, 32, v3
+; SI-NEXT:    v_lshlrev_b32_e32 v2, v3, v2
+; SI-NEXT:    v_ashrrev_i32_e32 v2, v3, v2
 ; SI-NEXT:    buffer_store_dword v2, v[0:1], s[0:3], 0 addr64
 ; SI-NEXT:    s_endpgm
 ;
@@ -234,7 +240,9 @@ define amdgpu_kernel void @v_sbfe_sub_i32(ptr addrspace(1) %out, ptr addrspace(1
 ; VI-NEXT:    v_mov_b32_e32 v1, s1
 ; VI-NEXT:    v_add_u32_e32 v0, vcc, s0, v2
 ; VI-NEXT:    v_addc_u32_e32 v1, vcc, 0, v1, vcc
-; VI-NEXT:    v_bfe_i32 v2, v3, 0, v4
+; VI-NEXT:    v_sub_u32_e32 v2, vcc, 32, v4
+; VI-NEXT:    v_lshlrev_b32_e32 v3, v2, v3
+; VI-NEXT:    v_ashrrev_i32_e32 v2, v2, v3
 ; VI-NEXT:    flat_store_dword v[0:1], v2
 ; VI-NEXT:    s_endpgm
   %id.x = tail call i32 @llvm.amdgcn.workitem.id.x()

llvm/test/CodeGen/AMDGPU/extract-lowbits.ll

@@ -150,11 +150,21 @@ define i32 @bzhi32_c4_commutative(i32 %val, i32 %numlowbits) nounwind {
 ; ---------------------------------------------------------------------------- ;
 
 define i32 @bzhi32_d0(i32 %val, i32 %numlowbits) nounwind {
-; GCN-LABEL: bzhi32_d0:
-; GCN:       ; %bb.0:
-; GCN-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GCN-NEXT:    v_bfe_u32 v0, v0, 0, v1
-; GCN-NEXT:    s_setpc_b64 s[30:31]
+; SI-LABEL: bzhi32_d0:
+; SI:       ; %bb.0:
+; SI-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; SI-NEXT:    v_sub_i32_e32 v1, vcc, 32, v1
+; SI-NEXT:    v_lshlrev_b32_e32 v0, v1, v0
+; SI-NEXT:    v_lshrrev_b32_e32 v0, v1, v0
+; SI-NEXT:    s_setpc_b64 s[30:31]
+;
+; VI-LABEL: bzhi32_d0:
+; VI:       ; %bb.0:
+; VI-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; VI-NEXT:    v_sub_u32_e32 v1, vcc, 32, v1
+; VI-NEXT:    v_lshlrev_b32_e32 v0, v1, v0
+; VI-NEXT:    v_lshrrev_b32_e32 v0, v1, v0
+; VI-NEXT:    s_setpc_b64 s[30:31]
   %numhighbits = sub i32 32, %numlowbits
   %highbitscleared = shl i32 %val, %numhighbits
   %masked = lshr i32 %highbitscleared, %numhighbits