[RISCV] Implement MC relaxations for compressed instructions.

Summary:
     This patch implements relaxation for RISCV in the MC layer.
      The following relaxations are currently handled:
      1) Relax C_BEQZ to BEQ and C_BNEZ to BNEZ in RISCV.
      2) Relax and C_J $imm  to JAL x0, $imm  and CJAL to JAL ra, $imm.

Reviewers: asb, llvm-commits, efriedma

Reviewed By: asb

Subscribers: shiva0217

Differential Revision: https://reviews.llvm.org/D43055

llvm-svn: 326626

4 files changed, 151 insertions, 3 deletions

diff --git a/llvm/test/MC/RISCV/fixups-compressed.s b/llvm/test/MC/RISCV/fixups-compressed.s
index 65e4c773eca..a97d290f216 100644
--- a/llvm/test/MC/RISCV/fixups-compressed.s
+++ b/llvm/test/MC/RISCV/fixups-compressed.s
@@ -2,13 +2,15 @@
 # RUN:     | FileCheck -check-prefix=CHECK-FIXUP %s
 # RUN: llvm-mc -triple riscv32 -filetype=obj -mattr=+c < %s \
 # RUN:     | llvm-objdump -d - | FileCheck -check-prefix=CHECK-INSTR %s
+# RUN: llvm-mc -filetype=obj -mattr=+c -triple=riscv32 %s \
+# RUN:     | llvm-readobj -r | FileCheck %s -check-prefix=CHECK-REL
 
 .LBB0_2:
 # CHECK-FIXUP:   fixup A - offset: 0, value: .LBB0_2, kind: fixup_riscv_rvc_jump
 # CHECK-INSTR: c.j     0
 c.j     .LBB0_2
 # CHECK:   fixup A - offset: 0, value: func1, kind: fixup_riscv_rvc_jump
-# CHECK-INSTR: c.jal   0
+# CHECK-INSTR: c.jal   6
 c.jal   func1
 # CHECK-FIXUP:   fixup A - offset: 0, value: .LBB0_2, kind: fixup_riscv_rvc_branch
 # CHECK-INSTR: c.beqz  a3, -4
@@ -16,3 +18,8 @@ c.beqz  a3, .LBB0_2
 # CHECK-FIXUP:   fixup A - offset: 0, value: .LBB0_2, kind: fixup_riscv_rvc_branch
 # CHECK-INSTR: c.bnez  a5, -6
 c.bnez  a5, .LBB0_2
+
+func1:
+  nop
+
+# CHECK-REL-NOT: R_RISCV
diff --git a/llvm/test/MC/RISCV/relocations.s b/llvm/test/MC/RISCV/relocations.s
index 13c6b512f26..77421620e68 100644
--- a/llvm/test/MC/RISCV/relocations.s
+++ b/llvm/test/MC/RISCV/relocations.s
@@ -85,11 +85,13 @@ bgeu a0, a1, foo
 # FIXUP: fixup A - offset: 0, value: foo, kind: fixup_riscv_branch
 
 c.jal foo
-# RELOC: R_RISCV_RVC_JUMP
+# A compressed jump (c.j) to an unresolved symbol will be relaxed to a (jal).
+# RELOC: R_RISCV_JAL
 # INSTR: c.jal foo
 # FIXUP: fixup A - offset: 0, value: foo, kind: fixup_riscv_rvc_jump
 
 c.bnez a0, foo
-# RELOC: R_RISCV_RVC_BRANCH
+# A compressed branch (c.bnez) to an unresolved symbol will be relaxed to a (bnez).
+# RELOC: R_RISCV_BRANCH
 # INSTR: c.bnez a0, foo
 # FIXUP: fixup A - offset: 0, value: foo, kind: fixup_riscv_rvc_branch
diff --git a/llvm/test/MC/RISCV/rv32-relaxation.s b/llvm/test/MC/RISCV/rv32-relaxation.s
new file mode 100644
index 00000000000..66109faf3eb
--- /dev/null
+++ b/llvm/test/MC/RISCV/rv32-relaxation.s
@@ -0,0 +1,75 @@
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+c < %s \
+# RUN:     | llvm-objdump -d - | FileCheck -check-prefix=INSTR %s
+
+FAR_JUMP_NEGATIVE:
+  c.nop
+.space 2000
+
+FAR_BRANCH_NEGATIVE:
+  c.nop
+.space 256
+
+NEAR_NEGATIVE:
+  c.nop
+
+start:
+  c.bnez a0, NEAR
+#INSTR: c.bnez a0, 72
+  c.bnez a0, NEAR_NEGATIVE
+#INSTR: c.bnez a0, -4
+  c.bnez a0, FAR_BRANCH
+#INSTR-NEXT: bnez a0, 326
+  c.bnez a0, FAR_BRANCH_NEGATIVE
+#INSTR-NEXT: bnez a0, -268
+  c.bnez a0, FAR_JUMP
+#INSTR-NEXT: bnez a0, 2320
+  c.bnez a0, FAR_JUMP_NEGATIVE
+#INSTR-NEXT: bnez a0, -2278
+
+  c.beqz a0, NEAR
+#INSTR-NEXT: c.beqz a0, 52
+  c.beqz a0, NEAR_NEGATIVE
+#INSTR-NEXT: c.beqz a0, -24
+  c.beqz a0, FAR_BRANCH
+#INSTR-NEXT: beqz a0, 306
+  c.beqz a0, FAR_BRANCH_NEGATIVE
+#INSTR-NEXT: beqz a0, -288
+  c.beqz a0, FAR_JUMP
+#INSTR-NEXT: beqz a0, 2300
+  c.beqz a0, FAR_JUMP_NEGATIVE
+#INSTR-NEXT: beqz a0, -2298
+
+  c.j NEAR
+#INSTR-NEXT: c.j 32
+  c.j NEAR_NEGATIVE
+#INSTR-NEXT: c.j -44
+  c.j FAR_BRANCH
+#INSTR-NEXT: c.j 286
+  c.j FAR_BRANCH_NEGATIVE
+#INSTR-NEXT: c.j -306
+  c.j FAR_JUMP
+#INSTR-NEXT: j 2284
+  c.j FAR_JUMP_NEGATIVE
+#INSTR-NEXT: j -2314
+
+  c.jal NEAR
+#INSTR: c.jal 16
+  c.jal NEAR_NEGATIVE
+#INSTR: c.jal -60
+  c.jal FAR_BRANCH
+#INSTR-NEXT: c.jal 270
+  c.jal FAR_BRANCH_NEGATIVE
+#INSTR-NEXT: c.jal -322
+  c.jal FAR_JUMP
+#INSTR-NEXT: jal 2268
+  c.jal FAR_JUMP_NEGATIVE
+#INSTR-NEXT: jal -2330
+
+NEAR:
+  c.nop
+.space 256
+FAR_BRANCH:
+  c.nop
+.space 2000
+FAR_JUMP:
+  c.nop
diff --git a/llvm/test/MC/RISCV/rv64-relaxation.s b/llvm/test/MC/RISCV/rv64-relaxation.s
new file mode 100644
index 00000000000..018408f575a
--- /dev/null
+++ b/llvm/test/MC/RISCV/rv64-relaxation.s
@@ -0,0 +1,64 @@
+# RUN: llvm-mc -filetype=obj -triple riscv64 -mattr=+c < %s \
+# RUN:     | llvm-objdump -d - | FileCheck -check-prefix=INSTR %s
+
+FAR_JUMP_NEGATIVE:
+  c.nop
+.space 2000
+
+FAR_BRANCH_NEGATIVE:
+  c.nop
+.space 256
+
+NEAR_NEGATIVE:
+  c.nop
+
+start:
+  c.bnez a0, NEAR
+#INSTR: c.bnez a0, 56
+  c.bnez a0, NEAR_NEGATIVE
+#INSTR: c.bnez a0, -4
+  c.bnez a0, FAR_BRANCH
+#INSTR-NEXT: bnez a0, 310
+  c.bnez a0, FAR_BRANCH_NEGATIVE
+#INSTR-NEXT: bnez a0, -268
+  c.bnez a0, FAR_JUMP
+#INSTR-NEXT: bnez a0, 2304
+  c.bnez a0, FAR_JUMP_NEGATIVE
+#INSTR-NEXT: bnez a0, -2278
+
+  c.beqz a0, NEAR
+#INSTR-NEXT: c.beqz a0, 36
+  c.beqz a0, NEAR_NEGATIVE
+#INSTR-NEXT: c.beqz a0, -24
+  c.beqz a0, FAR_BRANCH
+#INSTR-NEXT: beqz a0, 290
+  c.beqz a0, FAR_BRANCH_NEGATIVE
+#INSTR-NEXT: beqz a0, -288
+  c.beqz a0, FAR_JUMP
+#INSTR-NEXT: beqz a0, 2284
+  c.beqz a0, FAR_JUMP_NEGATIVE
+#INSTR-NEXT: beqz a0, -2298
+
+  c.j NEAR
+#INSTR-NEXT: c.j 16
+  c.j NEAR_NEGATIVE
+#INSTR-NEXT: c.j -44
+  c.j FAR_BRANCH
+#INSTR-NEXT: c.j 270
+  c.j FAR_BRANCH_NEGATIVE
+#INSTR-NEXT: c.j -306
+  c.j FAR_JUMP
+#INSTR-NEXT: j 2268
+  c.j FAR_JUMP_NEGATIVE
+#INSTR-NEXT: j -2314
+
+NEAR:
+  c.nop
+
+.space 256
+FAR_BRANCH:
+  c.nop
+
+.space 2000
+FAR_JUMP:
+  c.nop